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UNIVERSITY  OF  CALIFORNIA  PUBLICATIONS 


COLLEGE  OF  AGRICULTURE 

AGRICULTURAL  EXPERIMENT  STATION 

BERKELEY,  CALIFORNIA 


CALIfORNIA  PLANT  DISEASES 


By  RALPH  E.  SMITH  and  ELIZABETH  H.  SMITH 


BULLETIN  No.   218 

(Berkeley,  Cal.,  June,  1911) 


SACRAMENTO 

W.    W.    SHANNON        -      -      -       -       SUPERINTENDENT    OF    STATE    PRTNTING 

1911 


Benj.  Ide  Wheeler,  Ph.D.,  LL.D.,  President  of  the  University. 

EXPERIMENT  STATION    STAFF. 

E.  J.  Wickson,  M.A.,  Director  and  Horticulturist. 

E.  W.  Hilgard,  Ph.D.,  LL.D.,  Chemist   (Emeritus). 

W.  A.  Setchell,  Ph.D.,   Botanist. 

Leroy  Anderson,  Ph.D.,  Dairy  Industry  and  Superintendent  University  Farm  Schools. 

M.  E.  Jaffa,  M.S.,  Nutrition  Expert,  in  charge  of  the  Poultry  Station. 

R.  H.  Loughridge,  Ph.D.,  Soil  Chemist  and  Physicist   (Emeritus). 

C.  W.  Woodworth,  M.S.,  Entomologist. 

Ralph  E.  Smith,  B.S.,  Plant  Pathologist  and  Superintendent  of  Southern  California 

Pathological  Laboratory  and  Experiment  Station. 
G.  W.  Shaw,  M.A.,  Ph.D.,  Experimental  Agronomist  and  Agricultural  Technologist,  in 

charge  of  Cereal  Stations. 

E.  W.  Major,  B.Agr.,  Animal  Industry,  Farm  Manager,  University  Farm,  Davis. 

F.  T.  Bioletti,  M.S.,  Viticulturist. 

B.  A.  Etcheverry,  B.S.,  Irrigation  Expert. 

George  E.  Colby,  M.S.,  Chemist  (Fruits,  Waters  and  Insecticides),  in  charge  of 
Chemical  Laboratory. 

H.  J.  Quayle,  A.B.,  Assistant  Entomologist,  Plant  Disease  Laboratory,  Whittier. 

W.  T.  Clarke,  B.S.,  Assistant  Horticulturist  and  Superintendent  of  University  Exten- 
sion in  Agriculture. 

H.  M.  Hall,  Ph.D.,  Assistant  Botanist. 

C.  M.  Haring,  D.V.M.,  Assistant  Veterinarian  and  Bacteriologist. 
John  S.  Burd,  B.S.,  Chemist,  in  charge  of  Fertilizer  Control. 

E.  B.  Babcock,  B.S.,  Assistant  Agricultural  Education. 
W.  B.  Herms,  M.A.,  Assistant  Entomologist. 

J.  H.  Norton,  M.S.,  Assistant  Chemist,  in  charge  of  Citrus  Experiment  Station,  River- 
side. 
W.  T.  Horne,  B.S.,  Assistant  Plant  Pathologist. 

J.  E.  Coit,  Ph.D.,  Assistant  Pomologist,  Plant  Disease  Laboratory,  Whittier. 
C.  B.  Lipman,  Ph.D.,  Soil  Chemist  and  Bacterioligist. 
R.  E.  Mansell,  Assistant  in  Horticulture,  in  charge  of  Central  Station  grounds. 

A.  J.  Gaumnitz,  M.S.,  Assistant  in  Cereal  Investigations,  University  Farm,  Davis. 

E.  H.  Hagemann,  Assistant  in  Dairying,  Davis. 

B.  S.  Brown,  B.S.A.,  Assistant  in  Horticulture,  University  Farm,  Davis. 

F.  D.   Hawk,  B.S.A.,  Assistant  in  Animal  Industry. 

J.  I.  Thompson,  B.S.,  Assistant  in  Animal  Industry,  Davis. 

R.  M.  Roberts,  B.S.A.,  University  Farm  Manager,  University  Farm,  Davis. 

J.  C.  Bridwell,  B.S.,  Assistant  Entomologist. 

C.  H.  McCharles,  B.S.,  Assistant  in  Agricultural  Chemical  Laboratory. 
N.  D.  Ingham,  B.S.,  Assistant  in  Sylviculture,  Santa  Monica. 

E.  H.  Smith,  M.S.,  Assistant  Plant  Pathologist. 
T.  F.  Hunt,  B.S.,  Assistant  Plant  Pathologist. 

C.  O.   Smith,  M.S.,  Assistant  Plant  Pathologist,   Plant  Disease  Laboratory,   Whittier. 

F.  L.  Yeaw,  B.S.,  Assistant  Plant  Pathologist,  Vacaville. 
F.  E.  Johnson,  B.L.,  M.S.,  Assistant  in  Soil  Laboratory. 
Charles  Fuchs,  Curator  Entomological  Museum. 

P.  L.  Hibbard,  B.S.,  Assistant  Fertilizer  Control  Laboratory. 

L.  M.  Davis,  B.S.,  Assistant  in  Dairy  Husbandry,  University  Farm,  Davis. 

L.  Bonnett,  I.S.,  Assistant  in  Viticulture. 

S.   S.  Rogers,  B.S.,  Assistant  Plant  Pathologist,   Plant  Disease  Laboratory,   Whittier. 

B.  A.  Madson,  B.S.A.,  Assistant  in  Cereal  Laboratory. 

Walter  E.  Packard,  M.S.,  Field  Assistant,  Imperial  Valley  Investigations,  El  Centro. 

M.   E.   Stover,  B.S.,  Assistant  in  Agricultural  Chemical  Laboratory. 

P.  L.  McCreary,  B.S.,  Laboratory  Assistant  in  Fertilizer  Control. 

F.  C.  H.  Flossfeder,  Field  Assistant  in  Viticulture,  Davis. 

E.  E.  Thomas,  B.S.,  Assistant  Chemist,  Plant  Disease  Laboratory,  Whittier. 

Anna  Hamilton,  Assistant  in  Entomology. 

Mrs.  D.  L.  Bunnell,  Secretary  to  Director. 

W.  H.  Volck,  Field  Assistant  in  Entomology,  Watsonville. 

E.  L.  Morris,  B.S.,  Field  Assistant  in  Entomology,   San  Jose. 

J.  S.  Hunter,  Field  Assistant  in  Entomology,  San  Mateo. 

J.  C.  Roper,  Patron  University  Forestry  Station,  Chico. 

John  T.  Bearss,  Foreman  Kearney  Park  Station,   Fresno. 

E.  C.  Miller,  Foreman  University  Forestry  Station,  Chico. 


CALIfORNIA  PLANT  DISEASES. 

By  Ralph  E.  Smith  and  Elizabeth  H.  Smith. 


An  important  part  of  the  work  of  every  agricultural  experiment 
station  consists  in  the  dissemination  of  useful  information,  as  well  as 
the  carrying  on  of  investigations  seeking  for  new  knowledge.  It  is  the 
former  phase  of  station  work  which  is  represented  in  the  present 
bulletin.  This  publication  is  intended  as  a  handbook  of  plant  diseases 
occurring  in  California,  giving  a  brief  description  of  the  nature  of  the 
principal  troubles,  together  with  directions  for  their  control.  Many 
miscellaneous  and  less  important  troubles  are  also  described,  the  plan 
being  to  record  all  plant  diseases  of  any  possible  interest  which  have 
been  observed  in  California  by  members  of  the  department. 

The  illustrations  are  all  original  in  this  department,  save  those 
illustrating  vine  diseases  reproduced  from  Bulletin  197  of  this  experi- 
ment station.  The  photographs  have  been  taken  by  various  members 
of  the  staff,  while  the  drawings  are  by  Miss  E.  H.  Smith. 

The  meaning  of  the  word  ' '  disease, ' '  as  it  applies  in  the  present  sense 
tc  plant  production,  is  decidedly  less  specific  than  the  conception  of  the 
same  word  as  applied  to  the  human  race  or  domestic  animals.  In  the 
latter  case  disease  may  be  defined  as  the  opposite  of  health,  and  health 
means  a  condition  of  normal  functional  activity  of  the  body.  In  the 
growing  of  cultivated  plants  or  "crops,'  however,  there  are  always 
two  distinct  objects  or  considerations  involved  for  successful,  satis- 
factory results.     These  are  as  follows : 

(1)  The  plant  must  make  a  vigorous  development  and  maintain  to  as 
great  an  extent  as  possible  that  condition  which  we  denote  as  "thrift. " 
In  almost  all  cases  of  crop  production  it  is  desirable  to  maintain  thrifty 
and  vigorous  growth.  This  corresponds  quite  closely  to  what  we  call 
"health' '  in  the  animal  body. 

(2)  Along  with  this  thrifty  condition  it  is  likewise  necessary  to 
attain  certain  arbitrary  qualities  or  characteristics  of  the  root,  stem, 
leaf,  flower,  fruit  or  seed,  such  characteristics  being  those  which  make 
the  product  of  the  plant  most  desirable  from  a  commercial  standpoint. 
Most  of  these  qualities  are  not  at  all  necessary  to  a  condition  of 
ordinary  health  or  thrift,  and  some  of  them  are  even  opposed  to  it. 

We  may,  therefore,  say  in  the  present  sense  that  we  are  considering 
under  the  term  "disease"  any  condition  of  a  plant  in  which  there  is 


.1040  UNIVERSITY   OF    CALIFORNIA — EXPERIMENT    STATION. 

a  decided  failure  of  thrifty  development,  or  failure  of  the  plant  to 
produce  a  commercial  product  of  satisfactory  quality  or  quantity. 

This  bulletin  will  impress  many,  at  first  sight,  as  being  of  a  much 
more  general  nature  and  wider  in  scope  than  the  usual  plant  disease 
manual.  It  may  seem  to  some  to  leave  the  province  of  the  plant 
pathologist  and  invade  that  of  the  soil  chemist  and  physicist,  the  agron- 
omist and  the  horticulturist.  Such  a  conception  of  the  scope  of  plant 
pathology  results  from  the  common  impression  that  all  plant  diseases 
are  caused  by  insects,  fungi,  bacteria  or  other  living  organisms  of  the 
nature  known  as  parasites.  This  is  far  from  being  the  case,  particu- 
larly in  a  region  like  California,  where  the  conditions  attending  the 
culture  of  plants  are  extremely  artificial,  the  soils  largely  in  a  semi- 
arid  or  desert  condition  before  being  brought  under  cultivation,  and 
where  the  commercial  crops  are  produced  by  plants  which  have  been 
introduced  from  all  sorts  of  climates  and  conditions.  Under  such 
circumstances  it  is  not  surprising  that  soil  and  climatic  conditions 
should  have  powerful  influences  upon  plant  growth,  and  produce 
many  abnormal  effects  and  disturbances.  Such  is  the  case,  and  in 
diagnosing  plant  troubles  in  California  it  is  quite  as  necessary  and 
usually  more  difficult  to  judge  such  influences  accurately  than  to  deter- 
mine the  work  of  parasitic  organisms.  Many  of  these  effects  can  not 
be  distinctly  segregated  or  described  as  specific  diseases  of  certain 
plants,  but  they  will  be  briefly  summarized  and  described  in  a  later 
chapter. 

The  development  of  plants  and  the  nature  of  the  products  which  they 
bear  are  influenced  by  two  principal  factors :  first,  the  inherent  quality 
of  the  plant  itself,  transmitted  through  the  seed  or  bud ;  second,  the 
nature  of  the  environment  in  which  the  plant  develops.  One  factor  is 
as  important  as  the  other,  and  the  plant  pathologist  must  work  through 
both  in  order  to  attain  the  desired  results.  In  the  former  case  he  enters 
the  field  or  calls  upon  the  services  of  the  plant  breeder,  in  order  to 
obtain  varieties  of  plants  having  the  desired  qualities,  while  in  the 
latter  case  he  investigates  the  effects  of  the  various  influences  and 
agencies  which  act  upon  the  plant  during  its  growth  and  seeks  means 
to  counteract  or  stimulate  such  influences,  as  the  case  may  be.  Here 
again  the  aid  of  various  sciences  must  be  invoked  in  order  to  obtain 
the  desired  results.  In  a  recent  text-book  the  matter  is  well  expressed 
in  the  following  language:  "Every  plant  has  definite  requirements  for 
its  best  development.  The  character  of  the  mature  plant  is  the  result 
of  two  sets  of  forces.  The  first  of  these  is  the  inherent  capacity  of  the 
seed  to  develop  and  produce  a  normal  individual  of  its  kind.  The 
second  set  of  forces  constitutes  the  environment  in  which  the  plant 
grows,  and  of  which  the  soil  is  one  part,  the  other  component  being 


Bulletin  218]  CALIFORNIA  PLANT  DISEASES.  1041 

climate.  Every  plant  is  an  expression  of  the  combination  and  inter- 
action of  these  three  groups  of  forces — the  seed,  the  climate,  and  the 
soil."* 

Ideal  conditions  for  the  production  of  any  crop  may  be  summarized 
as  follows: 

In  the  Plant : 

Proper  Inherent  Qualities  of  Growth  and  Production. 
In  the  Air  : 

Proper  Temperature ; 

Proper  Moisture  ; 

Proper  Light ; 

Proper  Chemical  Composition ; 

Freedom  from  Injurious  Influences. 

In  the  Soil : 

Proper  moisture  ; 
Proper  Aeration  ; 

Proper  Chemical  Composition  ; 

Proper  Physical  Composition ; 

Freedom  from  Injurious  Influences. 

In  other  words,  the  plant  needs  in  its  environment,  for  successful 
development,  a  proper  degree  of  heat,  moisture,  air,  light,  and  food,  and 
freedom  from  injurious  influences.  Any  serious  departure  from  these 
ideal  conditions  results,  in  the  present  sense,  in  disease. 

PLANT  PHYSIOLOGY. 

A  clear  understanding  of  the  fundamental  principles  of  normal  plant 
physiology  is  necessary  to  enable  one  to  judge  abnormal  or  diseased 
conditions  with  any  degree  of  accuracy.  A  brief  exposition  of  this 
subject  may,  therefore,  be  of  use  at  this  point. 

Every  plant  consists  of  certain  parts  or  organs,  each  with  its  parti- 
cular duty  to  perform  to  maintain  the  life  and  activities  of  the  whole. 
These  parts  are  commonly  as  follows :  The  root,  stem,  branch,  leaf, 
flower,  fruit  and  seed.  Any  or  all  of  these  parts  is  liable  to  disease, 
either  in  the  strict  sense  of  the  word,  meaning  that  they  may  be  so 
affected  as  to  cause  an  unhealthy  condition,  or  they  may  be  affected  in 
the  broader  sense  of  having  undesirable  commercial  characteristics, 
since  all  of  these  parts,  in  various  plants,  represent  the  commercially 
desirable  portion.  Some  plants,  for  instance,  like  the  turnip  or  carrot, 
are  cultivated  for  the  root,  some  for  the  stem  or  branches,  like  the 
asparagus  or  celery,  some  for  the  leaf,  like  the  lettuce,  and  a  great  many 
different  kinds  for  the  flowers,  fruit,  or  seed.  If  the  root  or  stem  be 
diseased,  in  a  sense  of  being  in  an  injured  or  unhealthy  condition,  the 
flowT  of  water  from  the  ground  will  be  cut  off  or  interfered  with  and  the 
remainder  of  the  plant  suffer  accordingly.  If  the  leaves  are  injured 
or  destroyed  their  functions  will  be  interfered  with  and  the  rest  of  the 

*  Soils.     Lyon  and  Fippin. 


1042 


UNIVERSITY    OF    CALIFORNIA — EXPERIMENT    STATION. 


plant  suffer  from  starvation.  Likewise,  the  value  of  the  crop  will  be 
injured  or  destroyed  if  the  particular  part  of  which  the  plant  is 
cultivated  has  imperfections  or  undesirable  characteristics,  whether 
the  health  or  thrift  of  the  plant  is  injured  or  not. 


Fig.  1. — Diagram  of  tree  showing  movements  of  fluids  as  shown  by 

arrows. 


Of  the  organs  mentioned,  the  root  commonly  grows  in  the  soil  and 
the  remainder  of  the  plant  in  the  air. 


Bulletin  218]  CALIFORNIA  plant  DISEASES.  1043 

SOIL  RELATION. 

The  soil  has  two  general  purposes  in  relation  to  plant  growth.  In 
the  first  place  it  furnishes  a  medium  through  which  the  root  is  able  to 
accomplish  its  mechanical  function  of  holding  the  plant  upright  in  the 
air  and  exposing  its  parts  to  the  air  and  sunlight.  Second  and  more 
important,  the  soil  is  a  storehouse  of  food  and  moisture,  both  of  which 
are  indispensable  to  plant  growth.  The  soil  is  composed  of  an  aggre- 
gation of  various  sized  particles  of  mineral  matter,  resulting  from 
the  disintegration  of  rocks,  into  which  is  mixed  various  amounts  of 
organic  matter,  resulting  from  the  decomposition  of  plant  and  animal 
remains.  Being  composed  of  individual  particles  of  irregular  shape 
there  is  more  or  less  space  between  these  particles,  which  is  filled  either 
with  water  or  with  air  and  other  gases.  The  size  of  the  spaces  and, 
therefore,  the  amount  of  water  or  air  which  the  soil  may  contain  depends 
upon  the  size  of  the  particles  and  the  degree  to  which  they  are  com- 
pacted together. 

Far  from  being  an  inert  mass  of  dead  mineral  and  organic  matter, 
the  soil  is  likewise  the  home  of  uncounted  myriads  of  living  organisms, 
not  only  soil  bacteria,  of  which  much  has  been  heard  of  late,  but  also 
many  other  forms  of  low  plant  life,  hosts  of  simple  animal  organisms, 
and  likewise  more  highly  developed  creatures,  such  as  earth  worms  and 
many  other  forms.  All  of  these  exert  a  profound  influence  upon  the 
soil  and  its  relation  to  plant  production. 

The  features  of  the  soil  which  particularly  interest  us  in  this  connec- 
tion have  three  phases :  chemical,  physical  and  biological.  Chemically, 
the  soil  furnishes  most  of  the  elements  of  food  which  the  plant  requires, 
said  elements  being  derived  from  the  original  rocks  from  which  the  soil 
was  formed  and  the  decaying  plant  and  animal  remains  which  it 
contains,  all  being  gradually  brought  into  solution  in  the  water  which 
permeates  the  soil.  The  soil  may  likewise  contain  substances  of  a 
nature  injurious  to  plants.  It  is,  therefore,  most  evident  that  the 
student  of  plant  pathology  must  carefully  consider  the  chemical  nature 
of  the  soil  in  studying  the  condition  and  health  of  the  plant. 

Physically,  the  texture  of  the  soil  has  a  very  great  influence  upon  the 
development  of  the  root,  upon  the  supply  of  moisture  which  the  soil  may 
furnish  to  the  plant,  upon  the  availability  and  accessibility  of  the  food 
supply  stored  up  in  the  soil,  upon  the  performance  of  cultural  opera- 
tions necessary  to  the  proper  development  of  the  plant  and  is  in  every 
way  fully  as  important  as  the  chemical  consideration. 

Biologically,  both  the  chemical  and  physical  condition  of  the  soil  are 
largely  influenced  by  the  activities  of  the  living  organisms  which  it 
contains,  and  this  relation  is  of  great  importance  in  many  ways  to  the 
growth  of  the  plant.     We  need  not  consider  these  matters  in  further 


1044 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION. 


detail  in  this  place  more  than  to  call  attention  to  their  fundamental 
importance. 

The  root  of  the  plant  spreads  through  the  soil  by  growth  and  subdivi- 
sion, forming  a  network  of  line  branches,  the  extremities  of  which  are 
the  delicate,  minute  root  hairs  through  which  food  and  water  are 
absorbed  (Fig.  2).  Air  is  also  required  by  the  root  as  well  as  by  other 
parts  of  the  plant.     The  activities  of  the  root  are  therefore  entirely 

dependent  upon  the  physical 
texture,  moisture  supply,  tem- 
perature and  chemical  composi- 
tion of  the  soil.  If  these  con- 
ditions are  favorable,  the  plant 
flourishes  so  far  as  the  func- 
tions of  the  root  are  concerned. 
If  decidedly  unfavorable  in 
any  important  respect,  bad 
results  or  disease  follow. 

The  specific  food  substances 
taken  from  the  soil  by  the  root 
are  as  follows :  Nitrogen,  hy- 
drogen, sulphur,  phosphorus, 
calcium,  potassium,  iron,  mag- 
nesium and  oxygen.  Some  of 
these  elements  may  be  replaced 
to  some  extent  by  others,  as,  for 
instance,  sodium  and  calcium 
may  partly  take  the  place  of 
potassium  and  magnesium. 
Other  non-essential  substances 
may  also  be  taken  up,  and  in- 
deed it  may  be  said  that  almost 
any  element  in  the  soil  may  be 
absorbed  in  considerable  quan- 
tities. All  these  elements  are 
absorbed  by  the  plant  through 
the  root  in  the  form  of  a  solu- 
tion in  wrater.  In  other  words,  the  water  of  the  soil  is  a  weak  solution 
of  these  and  any  other  soluble  substances  which  the  soil  may  contain. 
Each  of  these  substances,  with  the  exceptions  stated,  is  indispensable  to 
the  growth  of  ordinary  plants.  In  other  words,  the  plant  is  unable  to 
develop  if  any  one  of  these  be  lacking.  Some  of  them  are  needed  only 
in  very  small  amount,  and  we  can  scarcely  imagine  a  soil  which  would 
be  entirely  deficient  in  any  one  of  these  elements.     Soils  differ,  how- 


Fig.  2. — Root    hairs    in    soil. 


Bulletin  21S] 


CALIFORNIA    PLANT    DISEASES. 


1045 


ever,  in  the  relative  amounts  of  these  substances  which  they  contain 
and  there  is  likewise  a  great  difference  in  the  amounts  of  them  which 
are  demanded  by  plants.  The  three  elements  most  likely  to  be  lacking 
in  quantities  sufficient  for  the  maximum  development  of  plants  are 
nitrogen,  phosphorus  and  potassium.  Less  commonly  calcium  (lime) 
is  lacking,  and  in  some  instances  an  addition  of  iron  to  the  soil  shows  a 
beneficial  effect  upon  the  growth  of  plants. 


A    B  C        D  E 

Fig.  3. — Section    of   tree    trunk.     A   outer   bark,    B    inner   bark, 
C  cambium,  D  sap  wood,  E  heart  wood. 

The  chemical  nature  of  the  soil  and  its  modification  by  the  addition 
of  various  substances  in  the  practice  of  fertilization  or  soil  modification, 
form  a  very  complicated  subject  in  regard  to  its  effect  upon  the  growth 
of  plants.  Such  effects,  while  sometimes  comparatively  simple  and 
consisting  merely  in  a  direct  addition  to  the  supply  of  food  material 
taken  up  by  the  plant,  are  often  extremely  indirect,  and  the  ultimate 
effect  upon  the  plant  may  come  about  through  the  chemical  action  of  the 


1046  UNIVERSITY   OF    CALIFORNIA — EXPERIMENT    STATION. 

material  upon  other  chemical  substances  in  the  soil,  its  effect  upon  living 
organisms,  or  in  various  other  ways.  We  may  cite  here,  for  example, 
the  recent  discussions  which  have  come  up  in  southern  California  in 
regard  to  the  ratio  of  lime  and  magnesia  contained  in  soils,  the  injurious 
effects  upon  plant  life  of  certain  combinations  of  this  sort,  and  the  pos- 
sibilities of  correcting  such  troubles  by  the  addition  of  lime  or  magnesia 
to  the  soil. 

From  the  standpoint  of  the  plant  pathologist,  the  chemical  nature 
of  the  soil,  through  which  most  of  the  physical  and  biological  effects  are 
ultimately  expressed,  has  three  main  considerations:  first,  the  limiting 
of  growth  by  a  deficiency  in  one  or  more  necessary  constituents,  includ- 
ing water;  second,  a  possibility  of  injurious  effects  resulting  from  the 
presence  in  the  soil  of  certain  substances  in  excessive  amounts;  third, 
specific  effects  of  the  chemical  elements  of  the  soil  upon  the  character 
of  the  commercial  product  of  the  plant,  such,  for  instance,  as  the  color, 
fiavor  or  texture  of  the  fruit.  In  other  words,  the  question  arises  in 
numerous  instances  as  to  whether  poor  growth,  lack  of  fruit  production, 
deficiency  in  size,  or  some  other  partial  failure  may  be  due  to  a  lack  or 
an  excess  of  some  substance  in  the  soil,  and  also  to  what  extent  arbi- 
trary characteristics  in  the  commercial  product  such  as  color,  flavor,  or 
texture  may  be  influenced  by  chemical  treatment  or  the  chemical  nature 
of  the  soil.  This,  in  California,  is  one  of  the  most  important  phases  of 
our  subject. 

Another  feature  of  the  soil,  which  relates  to  plant  physiology,  is  its 
temperature,  a  factor  which  may  be  of  some  importance. 

MOVEMENTS  OF  FLUIDS. 

After  being  absorbed  by  the  root  the  soil  solution,  or  as  we  may  now 
call  it  the  sap,  passes  upward  into  the  plant  from  the  smaller  into  the 
main,  larger  roots,  on  up  into  the  trunk.  The  particular  path  of  this 
upward  stream  is  located  in  the  xylem  or  woody  portion  of  the  conduct- 
ing fibers;  in  woody  trees  of  considerable  size  this  upward  flow  of  sap 
from  the  roots  is  most  active  in  the  newer,  outer  layers  of  wood  or  what 
we  call  the  ' '  sap  wood. ' '  Very  large  amounts  of  water,  with  food  mate- 
rials in  solution,  pass  up  through  the  stems  of  plants  in  this  way,  as  may 
readily  be  seen  when  we  consider  the  amount  of  the  soil  elements  which 
plants  contain,  and  the  fact  that  the  solution  in  which  they  come  into  the 
plant  from  the  soil  is  an  extremely  dilute  one.  A  large  supply  of  water 
is  therefore  necessary  and  indispensable  to  the  growth  of  the  plant,  not 
only  for  its  actual  use  as  food,  but  also  as  a  conveyor  of  other  elements, 
and  likewise  to  maintain  the  turgidity  or  rigidity  of  the  whole  plant 
body.  We  may  say,  indeed,  that  up  to  a  certain  point  the  growth  of  a 
plant  is  proportionate  to  the  amount  of  water  which  it  receives,  since 
the  more  water  the  soil  contains  the  more  food  material  will  be  dissolved 


Bulletin  218] 


CALIFORNIA   PLANT   DISEASES. 


1047 


and  given  entry  to  the  root.  Beyond  a  certain  point  the  soil  may 
receive  too  much  water,  aeration  be  too  much  reduced,  and  the  roots 
become  sluggish,  injured,  or  even  killed.  Under  the  semi-arid  condi- 
tions of  California,  however,  nothing  is  so  striking  in  regard  to  plant 
life  as  the  marvelous  effect  of  an  abundant  water  supply  upon  growth 
and  fruit  production.  The  crude  sap  solution  passes  along  up  through 
the  wood  or  xylem  of  the  stem  out  into  the  branches  and  finally  reaches 
the  leaves. 


—  S 


Fig.  4. — Cross  section  of  leaf,  ep  upper  epidermis, 
sm  and  st  sugar  and  starch-making  cells,  vb  fibro- 
vascular  bundle,  s  stoma. 


AIR  RELATION. 

The  relation  of  the  plant  to  the  atmosphere  which  surrounds  it  is  of 
supreme  importance,  its  relation  being  expressed  most  largely  through 
the  leaves,  which  act  as  organs  both  of  absorption  and  excretion.  The 
water  supply  coming  from  the  roots,  with  its  food  elements  in  solution, 
comes  into  the  leaves  and  there  the  larger  portion  of  the  water  is 
evaporated  off  into  the  air  by  the  process  called  transpiration.  This 
excess  of  water  passes  off  in  the  form  of  vapor,  reaching  the  air  through 
minute  openings  called  stomata  in  the  leaf  surface.  These  are  usually 
more  abundant  on  the  lower  than  on  the  upper  surface  of  the  leaf,  and 
in  the  leaves  of  some  plants  are  confined  entirely  to  the  lower  portion. 


1048  UNIVERSITY    OF    CALIFORNIA — EXPERIMENT    STATION. 

At  the  same  time  that  this  process  is  going  on  the  leaves  absorb  large 
quantities  of  carbon  from  the  air  in  the  form  of  carbon  dioxide  gas. 
Carbon  completes  the  list  of  food  substances  necessary  to  the  plant, 
taken  together  with  those  mentioned  as  being  derived  from  the  soil. 
The  leaves  are  able,  by  means  of  a  process  exerted  through  the  influence 
of  sunlight  upon  their  green  coloring  material  or  chlorophyll,  to 
decompose  this  carbon  dioxide  and  bring  the  carbon  into  combination 
with  hydrogen  and  oxygen  derived  from  the  soil.  As  a  result  of  this 
process,  which  is  called  photosynthesis,  a  succession  of  chemical  changes 
occurs  which  results  in  the  formation  of  sugar  in  the  leaf,  followed  by 
large  quantities  of  starch.  This  process  goes  on  during  sunlight,  and 
is  indispensable  to  the  life  of  the  plant.  During  active  sunlight  in  the 
daytime  a  large  excess  of  these  substances  is  formed,  so  that  by  evening 
the  leaf  contains  an  accumulation  of  starch  and  sugar.  Meantime,  both 
day  and  night,  the  starch  is  digested  into  sugar,  and  a  solution  of  the 
latter  substance  is  continually  being  distributed  from  the  leaves  to  all 
parts  of  the  plant  where  growth  is  taking  place  or  where  food  material 
is  being  stored  up.  This  current  passes  largely  through  vessels  called 
the  sieve  tubes,  which  in  woody  plants  are  located  in  the  inner  bark. 

Before  the  materials  formed  by  photosynthesis  can  be  assimilated  by 
living  substance,  they  are  formed  into  new  compounds  containing 
nitrogen.  A  variety  of  complicated  chemical  processes  goes  on  all  over 
the  plant  in  which  use  is  made  of  the  various  materials  taken  from  the 
soil,  and  the  various  substances  formed  build  up  the  growth  of  new 
parts,  the  formation  of  fruit,  or  are  otherwise  made  use  of  in  the 
activities  of  the  plant. 

Respiration  goes  on  in  the  leaves  in  a  manner  chemically  similar  to 
that  in  animals.     Oxygen  is  taken  in  and  carbon  dioxide  given  off. 

RELATION  OF  THE  PLANT  TO  CLIMATIC  CONDITIONS. 

The  atmosphere  has  many  relations  to  the  growth  of  plants  other 
than  that  of  supplying  carbon  dioxide  and  oxygen  to  the  leaves.  Its 
temperature,  for  instance,  is  one  of  the  most  important  factors  in  con- 
trolling the  distribution  of  plants  or  the  choice  of  location  where  certain 
species  can  be  grown.  The  humidity  of  the  air,  its  degree  of  moisture  or 
dryness,  is  also  of  considerable  importance.  The  degree  of  light  which 
the  leaves  receive  is  a  very  important  matter,  especially  as  it  influences 
the  process  of  photosynthesis,  which  is  the  first,  fundamental  operation 
in  the  nutrition  of  the  plant.  The  air  may  also  contain  substances 
injurious  to  vegetation,  although  this  rarely,  if  ever,  occurs  naturally. 


Bulletin  218]  CALIFORNIA  PLANT  DISEASES.  1049 

CAUSES  OF  PLANT  DISEASE. 

Non-Parasitic  Troubles. 
Atmospheric : 

Excessive  Cold  ; 

Excessive  Heat ; 

Excessive  Dryness  ; 

Excessive  Moisture ; 

Wind ; 

Hail; 

Artificial  Influences. 
Soil: 

Deficiency  of  Necessary  Substances  ; 

Excess  of  Certain  Substances   (Alkali,  Salt,  Acid)  ; 

Excessive  Dryness  ; 

Excessive  Moisture ; 

Faulty  Physical  Structure    (Hard-pan,   Heavy  or  Coarse  subsoil)  ; 

Artificial  Influences. 
Parasitic  Troubles. 

Higher  Animals    (Gophers,   Moles,    Squirrels)  ; 

Insects ; 

Worms ; 

Mollusks   (Slugs,  Snails)  ; 

Higher  Plants    (Dodder,  Mistletoe)  ; 

Fungi ; 

Bacteria ; 

Slime  Moulds. 

The  above  table  indicates  most  of  the  influences  which  affect  plants 
injuriously  in  California,  so  far  as  they  can  be  definitely  tabulated.  It 
should  be  further  mentioned  that,  in  many  cases,  various  combinations 
of  the  above  have  disastrous  results  which  could  not  be  attributed  to  any 
influence  acting  alone. 

DIRECTIONS    FOR   EXAMINATION    OF    DISEASED    PLANTS. 

Before  proceeding  to  a  description  of  the  principal  troubles  of  our 
various  crops  it  may  be  useful  to  give  the  following  general  directions 
for  the  examination  of  unhealthy  plants : 

1.  Note  whether  any  particular  portion  of  the  orchard  or  field  shows 
the  trouble  worse  or  less  and,  if  so,  seek  to  find  wherein  conditions  are 
different  there  from  those  in  the  remainder  of  the  planting. 

2.  Note  whether  any  particular  kind  or  variety  of  the  crop  is  more  or 
less  affected  than  others,  also  whether  any  particular  individuals  show 
marked  resistance,  immunity  or  freedom  from  the  trouble.  Ascertain 
the  commercial  qualities  and  desirability  of  any  seemingly  resistant  or 
immune  variety  or  individuals. 

3.  Determine  as  accurately  as  possible  the  part  of  the  plant  which  is 
actually  affected.  In  many  cases,  for  instance,  the  leaves  or  top  may 
wilt  and  die  when  the  real  trouble  is  in  the  roots. 

4.  Look  first  for  the  simplest  effects,  such  as  those  of  animals,  frost  or 
other  climatic  influences,  simple  injuries  or  other  obvious  causes  of 
trouble. 


1050  UNIVERSITY   OF    CALIFORNIA — EXPERIMENT   STATION. 

5.  Look  for  indications  of  alkali,  salt,  poor  drainage,  too  light  or  too 
heavy  soil  or  other  injurious  soil  conditions,  as  shown  by  surface  incrus- 
tations, the  occurrence  of  native  vegetation  peculiar  to  certain  conditions 
or  any  peculiarity  in  the  appearance  of  the  soil  in  the  region  of  the 
affected  plants. 

6.  Look  for  the  presence  of  fungi,  insects  or  other  parasites,  so  far  as 
one's  ability  extends  in  this  direction.  Endeavor  to  observe  accurately 
and  judge  intelligently  whether  the  organisms  found  are  the  cause  of 
the  trouble  or  simply  secondary. 

7.  If  nothing  is  found  above  ground  to  indicate  the  cause  of  the 
trouble,  dig  or  bore  a  hole  to  the  depth  reached  by  the  lowest  roots. 
During  the  digging  notice  the  condition  of  the  roots,  the  consistency  of 
the  layers  of  soil,  the  amount  of  moisture  which  they  contain,  and  their 
relation  to  the  development  of  the  roots.  Look  carefully  for  any 
peculiar  or  suspicious  condition,  either  in  the  roots  or  soil,  and  continue 
the  examination  out  to  the  smallest  roots  and  down  to  an  ample  depth. 

8.  Ascertain  as  closely  as  possible  all  that  can  be  found  out  about  the 
previous  history  and  treatment  of  the  soil  and  plants,  all  information 
of  possible  value  as  to  irrigation  practice,  fertilization,  cultural  methods 
and  previous  climatic  conditions ;  also  the  nature  of  the  trouble  from  its 
very  first  appearance. 

9.  If  necessary,  examine  healthy  groves,  trees  or  plants  of  the  same 
kind,  making  the  same  examinations  and  inquiries,  and  endeavor  to 
ascertain  wherein  conditions  differ  from  those  where  the  trees  or  plants 
are  diseased. 

After  this  examination,  if  more  information  is  desired,  endeavor  to 
select  the  most  characteristic  samples,  either  of  parts  of  the  plant  or 
soil,  and  send  them  to  the  proper  authority  with  complete  information 
as  to  the  nature  and  occurrence  of  the  trouble.  In  sending  parts  of 
plants,  pack  them  so  that  they  will  remain  as  fresh  as  possible.  In 
obtaining  soil  samples  take  a  fair  sample  from  each  foot  down  to  a  depth 
of  four  feet. 


Bulletin  218]  CALIFORNIA  PLANT  DISEASES.  1051 


SOME  OF  THE  MOST  COMMON  EEEECTS  OE  INJURIOUS  ATMOSPHERIC 
AND  SOIL  CONDITIONS  IN  CALIFORNIA. 

ATMOSPHERIC  INFLUENCES. 

Frost  and  Cold. — The  effects  of  low  temperature,  in  most  of  the  culti- 
vated portions  of  California,  are  only  such  as  are  produced  by  infre- 
quent frosts  or  injurious  effects  of  temperatures  very  little  below  the 
freezing  point  and  lasting  usually  but  a  few  hours.  Such  effects  are  in 
most  cases  evident  and  unmistakable,  needing  no  detailed  description 
and  resulting  simply  in  the  death  of  the  parts  or  organs  which  are 
severely  frozen.  This  is  seen,  for  instance,  in  the  not  infrequent  killing 
of  fruit  blossoms  and  young  shoots  by  late  spring  frosts,  the  nipping 
back  of  young  and  tender  growth  of  citrus  trees  during  occasional  cold 
nights  in  the  winter,  and  other  similar  effects.  In  regard  to  such 
injuries,  the  grower  was  formerly  at  the  mercy  of  the  elements,  depend- 
ing for  protection  only  upon  choice  of  location  in  planting  and  avoiding 
places  known  to  be  dangerous  for  a  certain  crop  on  account  of  likelihood 
to  frost.  In  comparatively  recent  times,  however,  appliances  and  meth- 
ods of  frost  protection  have  received  much  attention,  and  a  high  degree 
of  satisfaction  has  been  obtained.  By  the  development  of  such  methods, 
the  culture  of  some  of  our  more  tender  plants  has  been  extended  into 
regions  hitherto  dangerous. 

One  of  the  most  difficult  frost  injuries  to  detect  is  the  slight  freezing 
of  oranges,  which  occurs  now  and  then  in  some  sections.  When  this 
happens  the  internal  texture  of  the  fruit  is  injured,  its  juice  partially 
disappears,  and  a  greater  or  less  portion  of  the  pulp  of  the  orange 
becomes  dry  and  insipid.  Fruit  which  is  badly  affected  in  this  way 
may  be  readily  detected  in  handling  by  the  experienced  sorter,  but  occa- 
sionally there  may  be  a  considerable  quantity  of  slightly  affected  fruit 
which  is  extremely  difficult  of  detection  until  the  oranges  reach  the  con- 
sumer. A  specific  gravity  method  has  been  employed  to  some  extent, 
eliminating  all  the  oranges  which  float  in  a  liquid  of  a  certain  density. 
This  method  works  somewhat  to  the  disadvantage  of  the  producer,  taking 
out  all  the  lighter  oranges,  whether  frozen  or  not. 

Another  somewhat  obscure  effect  of  freezing  is  seen  occasionally  in 
young  citrus  and  other  trees  in  a  killing  of  the  inner  bark  just  above  the 
surface  of  the  ground.  Not  infrequently  young  trees,  which  appear  to 
have  gone  through  the  winter  without  harm,  as  indicated  by  the  appear- 
ance of  the  top,  begin  to  fail  and  die  later  in  the  spring,  and  on  exam- 
ination it  is  found  that  the  inner  bark  and  wood  in  the  vicinity  of  the 
cambium  layer  are  entirely  dead  for  some  distance  just  above  ground. 

In  the  case  of  deciduous  fruits  (see  Almond,  Apricot,  Cherry,  Peach 
and  Pear),  severe  frost  just  after  the  fruit  has  set  sometimes  kills  the 


1052  UNIVERSITY   OF    CALIFORNIA — EXPERIMENT    STATION. 

young  germ  of  the  seed  without  causing  the  fruit  to  drop  or  even  check- 
ing its  growth  for  some  time.  Such  fruit  sometimes  reaches  considerable 
size  before  falling  and  is  then  found  to  contain  a  black,  shriveled  seed 
germ,  killed  by  frost. 

In  citrus  districts  most  subject  to  low  temperatures  during  the  winter, 
with  occasional  severe  freezes,  there  sometimes  seems  to  occur  a  general 
lowering  of  the  vitality  of  the  trees,  and  an  appearance  of  weak,  un- 
healthy, mottled-leaf  condition.  In  such  regions  where  a  considerable 
portion  of  the  young  growth  of  the  trees  is  frequently  killed  back,  a 
condition  of  degeneration  lasting  all  through  the  season  may  occur, 
particularly  if  the  trees  do  not  receive  the  best  cultural  treatment. 

The  matter  of  frost  injury  in  most  parts  of  California,  where  the 
injurious  degree  of  temperature  is  very  slight,  its  duration  short,  and 
its  occurrence  comparatively  rare,  is  very  much  affected  by  compara- 
tively slight  influences,  particularly  the  condition  of  growth  in  the  plant 
and  the  degree  of  moisture  in  the  soil.  By  so  handling  the  crop  as  to 
keep  down  as  much  as  possible  the  production  of  tender  new  growth 
during  the  cold  season,  by  keeping  the  soil  in  moist  condition,  and  by  the 
use  of  the  comparatively  simple  protective  means  about  to  be  described, 
much  of  the  frost  damage  which  is  likely  to  happen  in  California  may 
be  prevented. 

Frost  prevention,  both  for  citrus  and  other  crops,  has  received  much 
attention  in  recent  years,  and  with  a  large  measure  of  success.  For  pre- 
venting damage  to  tender  growth,  fruit  or  blossoms  on  cold  nights, 
methods  have  been  perfected  which  consist  in  burning  smoky,  sooty 
fuel,  such  as  soft  coal  or  low  grade  oils,  in  numerous  small  receptacles 
placed  upon  the  ground  at  proper  intervals  whenever  the  temperature 
approaches  the  danger  mark.  A  variety  of  patented  devices  for  this 
purpose  is  upon  the  market,  and  literature  upon  the  same  may  be 
obtained  from  the  makers. 

In  the  case  of  young  trees,  particularly  citrus,  special  attention  is 
required  to  carry  them  through  the  first  three  or  four  years  in  localities 
subject  to  occasional  frosts.  The  damage  described  above,  where  the  tree 
is  killed  just  at  the  surface  of  the  ground,  and  likewise  the  killing  back 
of  the  top  is  successfully  prevented  by  banking  up  the  earth  somewhat 
about  the  trunk  in  the  fall,  and  by  the  use  of  a  wrapping  or  protector  of 
some  sort  about  the  trunk.  A  common  practice  with  citrus  trees  consists 
in  tying  several  cornstalks,  palm  leaves,  tule  or  similar  material  about 
the  trunk  of  sufficient  length  to  enclose  and  protect  most  of  the  top  of 
the  tree  at  the  same  time.  In  many  places  citrus  groves  have  been 
successfully  developed  by  thus  protecting  the  trees  during  their  first 
two  or  three  years  in  the  orchard,  when  without  such  protection  it  would 
have  been  almost  out  of  the  question  to  get  a  growth  started. 


Bulletin  218]  CALIFORNIA  plant  DISEASES.  1053 

Heat. — Cultivated  plants  in  some  portions  of  California  are  subjected 
to  very  extreme  degrees  of  heat  during  the  summer  time,  and  the  choice 
of  crops  for  certain  localities  is  largely  influenced  by  this  factor.  Be- 
yond this,  injury  from  unusual  degrees  of  heat,  particularly  when  com- 
bined with  extreme  atmospheric  dryness,  is  of  quite  frequent  occurrence. 
The  effect  of  this  is  usually  seen  in  a  sudden  burning  and  withering  of 
the  leaves,  producing  an  effect  sometimes  called  sun-scald.  Much 
damage  is  sometimes  caused  in  the  same  manner  to  fruit,  particularly 
grapes,  and  occasionally  some  of  the  deciduous  fruits.  This  injury 
shows  itself  as  a  burning  or  withering  of  the  fruit  on  the  exposed  side, 
or  a  shriveling  and  drying  of  the  fruit  before  it  reaches  full  size.  This 
trouble  is  frequently  seen  in  prunes  in  the  northern  part  of  the  State. 
Trouble  of  the  same  sort  is  also  common  with  the  English  walnut.  Quite 
frequently  an  unusually  hot,  dry  period,  particularly  when  the  crop  is 
approaching  maturity,  causes  a  withering  and  blackening  of  the  exposed 
sides  of  the  green  hulls  which  enclose  the  nuts,  and  this  burning  extends 
as  a  discoloration  into  the  meat  of  the  nut  itself,  causing  the  hull  to  stick 
to  the  nut  on  that  side,  and  the  nut  to  blacken,  both  inside  and  out.  This 
form  of  sunburn  often  causes  large  losses  to  the  walnut  grower,  and 
also  limits  the  growth  of  this  crop  to  regions  where  the  sun  is  not  too 
severe.' 

The  condition  of  weather,  commonly  known  in  this  State  as  a  "hot 
norther "  or  "  Santa  Ana, ' '  is  frequently  the  cause  of  much  damage  to 
some  crops,  especially  when  occurring  early  in  the  season.  The  condi- 
tion referred  to  consists  in  a  hot,  extremely  dry,  electrical  wind,  blowing 
from  the  interior  or  desert  portions  of  the  State  toward  the  coast. 
When  such  winds  occur  the  blossoms  of  fruit  trees  are  sometimes  killed 
and  young  sprouts  dried  up  and  destroyed,  the  latter  particularly  in  the 
case  of  buds  or  grafts  which  have  recently  been  put  in.  The  English 
walnut  is  also  particularly  susceptible  to  this  form  of  injury  when  in 
bloom.  The  damage  in  this  case  appears  to  be  done  mainly  to  the  pollen, 
and  if  this  sort  of  weather  occurs  just  when  the  catkins  are  shedding 
their  pollen,  the  setting  of  the  crop  may  be  very  seriously  affected. 

Another  condition  commonly  called  sunburn  is  of  frequent  occurrence, 
affecting  the  stems  or  trunks  of  young  trees.  This  is  almost  invariably 
seen  on  the  southwest  side  'Of  the  tree,  although  local  peculiarities  may 
influence  this  feature  somewhat.  The  trouble  is  due  to  a  killing  of  the 
cambium  layer  by  the  heat  of  the  sun  and  results  in  an  area  of  dead 
bark  extending  up  and  down  the  trunk  or  on  the  sides  of  larger  limbs, 
through  which  decay  often  sets  in  and  the  tree  is  badly  injured  or  killed. 
This  form  of  sunburn  is  seen  particularly  in  young  trees  recently  set  out, 
where  the  trunks  are  exposed  to  hot  sun  before  the  trees  have  been  able 
to  draw  a  plentiful  supply  of  moisture  from  the  soil  by  the  formation 

2— Bul.  218 


1054  UNIVERSITY   OF    CALIFORNIA — EXPERIMENT   STATION. 

of  new  roots.  Trees  which  for  any  reason  make  a  poor  start  and  fail 
to  root  properly  are  especially  liable  to  sunburn  in  the  trunk.  When, 
for  example,  nursery  trees  are  allowed  to  become  too  dry  before  planting 
this  frequently  occurs  and  the  trees  may  be  entirely  killed,  damaged  on 
one  side  or,  in  some  cases,  may  throw  out  new  shoots  from  the  lower 
portion  of  the  trunk. 

This  occurrence  of  sunburn  is  by  no  means  confined  to  the  summer 
season,  but  takes  place  even  more  commonly  during  the  winter  in  our 
climate.  Particularly  with  such  trees  as  the  walnut,  apple,  peach  and 
prune,  which  shed  their  leaves  in  the  winter,  the  sap  movement  does  not 
become  entirely  dormant  during  the  winter  but  is  kept  in  a  state  of  irreg- 
ular activity  by  the  occurrence  of  frequent  periods  of  warm  weather. 
Especially  in  regions  where  the  nights  are  fairly  cold  and  the  days  hot 
during  a  considerable  portion  of  the  winter,  trees  of  this  sort  become 
badly  sunburned.  The  sap  starts  and  stops  again  in  the  trunk  and 
without  the  presence  of  leaves  to  regulate  this  flow  in  a  normal  manner 
abnormal  conditions  occur  in  the  cambium  and  the  hot  afternoon  sun 
causes  a  burning  of  one  side  of  the  trunk.  Toadstool  or  other  fungi 
causing  decay  may  then  effect  an  entrance  through  such  a  wound  and 
the  tree  is  destroyed.  Sunburn  is  prevented  by  the  presence  of  an 
abundant  supply  of  moisture  in  the  soil  more  than  by  any  other  in- 
fluence. We  may,  of  course,  except  from  this  statement  the  influence 
of  shade,  or  climatic  conditions  not  conducive  to  damage  of  this  sort. 
Other  things  being  equal,  however,  trees  or  plants  having  an  abundant 
supply  of  moisture  in  the  ground  are  much  less  likely  to  suffer  from 
sunburn,  either  in  the  trunk  or  as  affecting  the  fruit.  It  is  therefore 
advisable  to  give  plants  and  trees  a  particularly  abundant  supply  of 
water  in  hot,  dry  times  when  the  fruit  may  be  kept  from  injury  by 
this  means,  and  also  during  the  fall  and  winter,  if  abundant  rains  do 
not  occur,  in  order  to  prevent  damage  to  the  trunks  and  buds.  In  the 
case  of  nursery  trees  which  have  become  too  dry  before  planting,  it  is 
often  advisable  to  cut  them  back  nearly  to  the  ground  and  allow  a  new 
shoot  to  come  up  and  form  the  trunk.  This  should  always  be  done 
when  the  tree  is  found  to  be  badly  sunburned  and  standing  in  a  dormant 
condition  without  throwing  out  any  new  growth.  By  thus  bringing  up 
a  fresh  shoot  from  below,  through  which  the  sap  is  able  to  circulate 
freely,  a  good,  thrifty  tree  is  often  produced,  while  if  the  tree  is  not  cut 
back  it  stands  all  through  the  season  throwing  out  a  few  stunted,  sickly 
shoots  from  its  sunburned  trunk  and  very  likely  dies  entirely. 

In  the  case  mentioned  of  deciduous  trees  which  become  sunburned 
in  the  trunk  during  the  winter  time  on  account  of  an  irregular  activity 
of  the  sap,  this  condition  is  usually  aggravated  if  the  surface  of  the  soil 
is  bare  and  free  from  vegetation.  Frequently  the  same  influences  which 
cause  sunburn  prevent  the  development  of  vegetation  on  such  soils,  on 


Bulletin  218]  CALIFORNIA  PLANT  DISEASES.  1055 

account  of  the  extreme  variation  in  temperature  in  winter  between  the 
day  and  the  night.  Heavy  frosts  occur  at  night,  freezing  the  surface 
of  the  ground,  while  the  hot  sun  of  the  day  heaves  it  up  and  destroys 
any  seedlings  which  may  have  started.  The  only  thing  which  can  be 
done  in  such  a  case  is  to  make  every  effort  to  get  some  sort  of  growth 
started  during  the  fall  before  the  coldest  nights  come  on.  This  is  fre- 
quently difficult  on  account  of  a  lack  of  water  for  starting  such  a  growth. 
If  it  is  not  feasible  the  next  best  thing  is  to  mulch  the  surface  of  the 
ground  about  the  trees,  covering  it  with  straw  or  any  similar  material 
which  may  be  available.  It  is  also  advisable  to  cover  the  trunks  and 
main  limbs  of  any  trees  which  are  in  danger  of  sunburn  with  a  coating 
of  thick  whitewash.  This  should  also  be  done  to  prevent  sunburn  wThen 
the  tops  of  trees  are  heavily  cut  back  for  any  purpose,  as.  for  instance, 
after  top-working  them  to  other  varieties. 

Before  leaving  the  subject  of  the  relation  of  temperature  to  vegeta- 
tion in  California,  we  may  say  that  many  peculiar  and  obscure  effects 
frequently  occur  as  a  result  of  bringing  plants  native  to  the  temperate 
zone  and  accustomed  to  a  definite  period  of  dormancy  during  the  winter, 
to  a  region  where  the  change  of  the  seasons  is  so  slightly  marked.  These 
plants  are  by  nature  accustomed  to  and  prepared  for  a  dormant  period 
during  a  portion  of  the  year.  They  not  only  drop  their  leaves  and 
cease  their  growth  at  the  approach  of  winter,  but  also  undergo  chemical 
and  various  other  physiological  changes  in  preparation  for  this  dormant 
period.  The  stimulation  or  irritation  caused  by  the  frequent  occurrence 
during  the  winter  of  weather  conditions  entirely  similar  to  those  normal 
to  the  spring  time,  must  cause  a  frequent  starting  and  stopping  again  of 
those  processes  which  go  on  in  the  tree  during  the  normal  commencement 
of  growth  in  the  spring,  and  in  this  way  pathological  conditions  are 
produced.  To  conditions  of  this  sort  appear  to  be  partially  due  such 
troubles  as  little  leaf  of  the  peach,  walnut  yellows,  sour  sap  of  stone 
fruits  and  possibly  other  of  the  so-called  physiological  or  climatic 
diseases.  The  only  relief  to  be  expected  from  this  trouble  is  through  the 
planting  of  species  or  varieties  of  fruit  which  are  known  to  be  unaffected 
by  such  disturbances. 

Excessive  Dryness. — This  subject  has  already  been  treated  in  connec- 
tion with  extremes  of  temperature.  High  temperature  in  California  is 
almost  invariably  accompanied  by  extreme  dryness  and  the  two  work 
together  in  producing  burning  of  foliage,  withering  of  fruit  and  similar 
effects. 

Excessive  Moisture. — Little  trouble  of  this  sort  is  experienced  in  Cali- 
fornia, since  no  rain  falls  during  most  of  the  growing  season  of  the 
majority  of  our  crops.  Fruit  setting  is  sometimes  prevented  by  violent 
or  long  continued  rains  during  the  blossoming  period,  this  result  being 


1056  UNIVERSITY   OF    CALIFORNIA — EXPERIMENT    STATION. 

produced  largely  by  interference  with  or  prevention  of  the  process 
of  pollination.  Most  of  our  deciduous  fruits  have  the  unfortunate 
habit  of  blooming  just  when  our  most  abundant  rains  are  likely  to  occur 
and  the  setting  of  fruit  is  sometimes  considerably  diminished  by  this 
means.  In  many  cases  also  imperfect  pollination  results  and  the  fruit 
either  falls  after  growing  for  a  short  time  or  the  seed  does  not  properly 
fill. 

Our  most  serious  effect  of  excessive  moisture  in  the  air  is  probably 
that  of  favoring  the  development  of  various  fungus  diseases  and  causing 
thus  an  indirect  injury.  It  is  an  almost  universal  rule  that  the  develop- 
ment of  parasitic  fungi  is  favored  by  atmospheric  moisture  and  very 
marked  differences  result  in  California  in  the  occurrence  of  plant 
diseases  in  various  seasons  according  to  the  amount  of  moisture  which 
occurs.  The  same  comparative  effect  is  seen  in  different  sections  of  the 
State,  the  same  crop  being  badly  affected  by  a  fungus  disease  in  one 
place  and  entirely  free  from  it  in  another,  as  a  result  of  a  difference  in 
atmospheric  moisture  conditions. 

Wind. — This  is  an  important  consideration  in  connection  with  Cali- 
fornia agriculture,  particularly  in  the  case  of  the  production  of  tree 
fruits.  In  choosing  a  location  for  an  orchard,  and  particularly  a  citrus 
grove,  this  feature  should  be  considered  along  with  temperature,  char- 
acter of  the  soil  and  water  supply.  The  bad  effects  of  wind  are  mostly 
mechanical,  consisting  in  a  bruising  of  the  fruit  by  contact  with  the 
branches  and  twigs.  More  than  this,  serious  loss  is  often  caused  in 
windy  localities  by  quantities  of  fruit  being  actually  blown  from  the 
trees  on  to  the  ground  before  it  is  ready  for  picking.  In  very  windy 
localities  the  growth  and  form  of  the  trees  are  decidedly  affected,  the 
tendency  usually  being  to  cause  the  tree  to  lean  over  and  make  its  prin- 
cipal growth  in  the  direction  of  the  prevailing  wind.  In  a  few  cases, 
notably  the  apricot  tree,  it  is  a  curious  fact  that  the  tree  shows  the 
opposite  response,  its  branches  curving  over  and  pointing  directly  into 
the  face  of  the  wind.  In  very  windy  localities,  particularly  along  the 
coast,  the  young  shoots  in  the  tops  of  the  trees  are  continually  killed 
back  by  the  wind,  which,  together  with  the  breaking  off  of  large  limbs, 
gives  the  trees  a  stunted  and  deformed  appearance.  Citrus  fruit  from 
windy  localities  loses  much  in  quality  on  account  of  being  covered  with 
scars  and  blemishes,  and  also  in  quantity,  as  just  stated,  on  account  of 
being  blown  from  the  trees. 

On  the  other  hand,  a  locality  otherwise  desirable  for  orcharding 
should  not  be  too  hastily  condemned  on  account  of  wind.  Most  parts 
of  California  are  comparatively  windy  in  their  primitive  state  on 
account  of  the  absence  of  trees  to  break  the  force  of  the  wind.  It  is  very 
noticeable  that  as  a  given  locality  or  valley  becomes  settled,  and  the 


Bulletin  218]  CALIFORNIA  PLANT  DISEASES.  1057 

country  is  broken  up  with  buildings  and  trees,  the  wind  currents  become 
less  severe  and  less  damage  results  from  this  cause  than  at  first.  In 
almost  all  orchard  planting  in  new  districts  this  fact  is  taken  into 
account,  and  protection  from  the  wind  is  attempted  and  attained  to  a 
more  or  less  extent  by  the  planting  of  rows  of  trees  called  wind-breaks. 
This  is  done  by  planting  close  rows  of  suitable  trees  at  intervals  across 
the  path  of  the  prevailing  wind,  on  the  windward  side  of  orchards,  or 
home  sites,  or  in  any  position  which  will  best  break  the  wind  in  the 
locality  where  protection  is  desired. 

For  this  purpose  eucalyptus  trees  have  been  most  commonly  used 
in  California,  particularly  the  blue  gum?  Eucalyptus  globulus,  in  all 
regions  adapted  to  its  growth.  It  is  customary  to  plant  these  trees 
about  eight  feet  apart,  using  two  or  three  rows  in  an  alternate  manner. 
Another  tree  much  used  for  wind-breaks  is  the  Monterey  cypress.  This 
makes  a  much  denser  growth  close  to  the  ground  than  eucalyptus,  and 
needs  to  be  planted  only  in  a  single  row.  Its  growth  is  slower  than 
that  of  the  blue  gum  but  rapid  compared  with  that  of  most  trees  other 
than  eucalyptus.  Often  a  combination  is  made  of  cypress  and  eucalyp- 
tus planted  alternately  in  a  single  row.  This  makes  a  taller  and  more 
rapid  growing  break  than  cypress  alone  and  a  denser  one  than  eucalyptus 
alone. 

Wind-breaks  have  a  serious  objection  on  account  of  the  large  amount 
of  moisture  and  plant  food  which  these  large,  rapid-growing  trees  take 
up.  With  eucalyptus,  particularly,  it  is  impossible  to  grow  thrifty 
fruit  trees  within  a  space  of  fifty  or  more  feet  of  the  wind-break  after 
the  trees  become  large.  The  shade  of  the  trees  also  has  a  detrimental 
effect  upon  the  neighboring  fruit  trees,  and  a  still  further  objection  is 
the  formation  of  so-called  frost  pockets,  the  latter  being  due  to  a  lack  of 
air  circulation  on  cold  nights  in  the  portions  of  the  grove  most  sheltered 
by  the  wind-break.  The  grower  must  decide  for  himself  in  individual 
cases  whether  the  benefit  of  such  a  planting  will  more  than  repay  its 
disadvantages.  There  is  a  marked  tendency  at  present  in  our  older 
settled  districts  to  cut  down  the  original  wind-breaks,  since  the  general 
development  of  the  country  has  broken  up  the  sweep  of  the  wind  and  the 
land  occupied  by  these  eucalyptus  or  other  trees  is  now  more  valuable  for 
fruit  trees  or  other  purposes. 

Hail. — Violent  hail  storms  are  of  occasional  occurrence,  even  in  the 
most  frost-free  portions  of  California.  Damage  is  sometimes  caused 
through  the  bruising  of  fruit  and  the  breaking  of  foliage  and  twigs. 

Artificial  Substances  in  the  Air. — We  have  already  said  that  the  atmos- 
phere never  contains  normally  anything  injurious  to  plants.  Fre- 
quently, however,  in  the  vicinity  of  cities  or  industrial  enterprises, 
various  emanations  are  poured  into  the  air  and  act  disastrously  upon 


1058  UNIVERSITY    OF    CALIFORNIA — EXPERIMENT    STATION. 

vegetation.  Such  effects  are  frequently  seen  in  the  vicinity  of  smelters, 
chemical  works,  or  in  localities  where  soft  coal  containing  large  amounts 
of  sulphur  is  burned.  Particularly  injurious  are  the  fumes  resulting 
from  the  burning  of  sulphur  in  any  form,  if  they  come  into  contact 
with  vegetation  without  being  very  much  diluted  with  air. 

The  subject  of  smelter  fume  injuries  has  received  very  extensive 
investigation  both  in  this  country  and  Europe  for  many  years.  This  has 
also  been  the  subject  of  a  vast  amount  of  expensive  litigation  between 
smelting  and  other  companies  on  the  one  hand,  and  agricultural  or 
timber  interests  on  the  other.  There  is  no  subject  which  needs  the  most 
competent  expert  attention  and  the  most  careful  judicial  consideration 
more  than  this.  Grave  and  extensive  injustice  may  be  done  by  an 
improper  finding  for  either  the  smelting  or  the  agricultural  interests. 
Both  industries  are  of  great  importance,  and  their  relative  rights  and 
standing  must  be  carefully  considered  in  cases  where  their  interests 
seem  to  clash.  From  the  standpoint  of  the  smelting  company,  there 
should  be  clearly  and  positively  established  the  amount  of  damage  which 
is  actually  being  caused  by  the  fumes  and  the  relative  value  of  the  agri- 
cultural interests  affected  in  proportion  to  that  of  the  smelting  and 
mining  interests.  There  is  invariably  a  very  natural  tendency  in  the 
vicinity  of  smelting  and  similar  plants  to  lay  to  the  smoke  all  sorts  of 
plant  and  animal  troubles,  real  and  imaginary,  which  are  not  caused 
by  any  other  very  obvious  agency.  In  all  agricultural  pursuits  there 
is  a  certain  element  of  uncertainty,  due  to  climate,  soil  conditions,  and 
other  uncontrollable  and  obscure  factors.  In  normal  districts  a  certain 
amount  of  animal  and  plant  disease,  crop  failure  and  similar  conditions 
is  expected  from  such  sources.  Given,  however,  a  specific,  ever-present 
agency,  known  to  be  injurious  under  certain  conditions,  and  it  is  a 
natural  tendency  to  lay  all  sorts  of  troubles  which  can  not  be  otherwise 
accounted  for  to  this  one  cause.  On  the  other  hand,  it  is  sometimes  the 
tendency  of  the  smelting  company,  partly  perhaps  in  self-protection,  to 
attempt  to  lay  all  troubles  and  injuries  to  effects  other  than  smoke,  and 
minimize  as  much  as  possible  the  damage  which  is  actually  caused. 

There  can  be  but  one  satisfactory  basis  of  settlement  of  all  such  cases, 
namely,  as  we  have  already  said,  a  careful,  expert,  and  unprejudiced 
examination  of  actual  conditions  and  a  settlement  of  damages  or  deter- 
mination of  future  policy  on  this  basis.  In  many  European  districts 
permanent  courts  or  arbitration  boards  have  been  established  under  state 
control  to  settle  these  questions  and  this  method  is  far  superior  to  a 
constant  wrangling  in  the  courts  with  final  decisions  based  on  the  relative 
arguing  ability  of  the  opposing  attorneys  or  the  influence  of  more  or 
less  incompetent,  so-called  experts,  subsidized  by  the  opposing  sides  to 
present  their  cases  in  the  best  possible  light.     If  this  matter  is  properly 


Bulletin  218] 


CALIFORNIA    PLANT    DISEASES. 


1059 


managed,  there  is  no  reason  why  agriculture  and  mining  should  not  both 
be  carried  on  to  mutual  advantage  and  without  antagonism. 

The  specific  effects  of  smelter  fumes  upon  vegetation  can  not  be  stated 
or  described  in  such  a  manner  as  to  make  their  identification  absolutely 
certain.  In  a  general  way  it  may  be  said  that  such  effects  consist  in  a 
spotting  or  burning  of  the  leaves,  and  we  may  also  say  that  there  can  be 
no  injury  without  such  spotting  or  burning.  In  other  words,  there  is 
no  such  thing  as  an  invisible  damage  to  plants  by  smelter  fumes.  Leaf 
spot,  however,  is  caused  by  so  many  other  agencies  and  conditions  that 


Fig.  5. — Effect    of    smelter    fumes    on    leaves    of    alfalfa. 


only  the  most  careful  local  examination,  and  broad,  general  knowledge 
of  other  effects  which  act  injuriously  upon  vegetation,  can  enable  one 
to  positively  distinguish  smoke  injury.  Microscopic  study  of  injured 
tissues  is  of  much  assistance  to  the  experienced  investigator,  but  here 
again  no  definite  symptoms  can  be  laid  down  which  distinguish  this 
injury  from  all  others.  Chemical  analysis,  also,  has  its  place,  but  does 
not  suffice  to  distinguish  arbitrarily  and  specifically  all  smelter  smoke 


1060  UNIVERSITY   OF    CALIFORNIA — EXPERIMENT    STATION. 

injury  from  every  other  possible  source  of  trouble.  One  having  a  gen- 
eral knowledge  of  plant  pathology  and  entomology  can  usually  soon 
eliminate  in  a  smoke  district  many  fungus,  bacterial  and  insect  effects 
which  have  been  ascribed  more  or  less  to  the  smoke,  but  beyond  this  he 
may  encounter  effects  of  frost,  unfavorable  soil  or  climatic  conditions, 
lack  of  proper  cultivation,  effects  of  fire  and  many  other  influences 
which  must  be  thoroughly  understood  and  considered.  On  the  other 
hand,  he  must  not  exaggerate  such  effects  as  these  and  attribute  to  them 
injuries  which  are  really  due  to  the  smoke. 

Different  species  of  plants  vary  widely  in  their  susceptibility  to  smoke 
injury,  and  the  amount  of  injury  is  also  decidedly  influenced  by  weather 
conditions.  Other  things  being  equal,  more  damage  to  vegetation  is 
caused  during  wet  than  in  dry  weather.  This  may  be  due  to  the  fact 
that  the  injurious  substances  are  absorbed  by  moisture,  and  thus  brought 
into  contact  with  vegetation  in  a  more  concentrated  form  when  it  is  wet. 
More  injury  is  caused  in  localities  where  the  wind  tends  to  blow  steadily 
in  one  direction  much  of  the  time  than  in  places  where  the  currents  of 
air  are  constantly  shifting.  In  the  latter  case,  a  fairly  concentrated 
smoke  may  cause  no  appreciable  damage,  while,  in  the  former,  quite 
dilute  fumes  may  mark  out  a  very  evident  path  of  destruction  on  the 
vegetation  in  the  direction  of  the  prevailing  wind. 

Damage  is  also  sometimes  caused  by  manufacturing  plants  which 
discharge  large  amounts  of  dust  into  the  atmosphere.  This  is  the  case 
in  the  manufacture  of  cement,  where  great  quantities  of  dust  go  out 
into  the  air  and  settle  upon  the  leaves  of  surrounding  vegetation,  the 
dust  often  setting  like  cement  to  a  considerable  extent.  This  is  very 
destructive  to  the  appearance  and  selling  quality  of  fruit  or  vegeta- 
bles upon  which  it  occurs,  and  in  the  case  of  trees,  particularly  ever- 
greens like  the  orange  and  lemon,  there  appears  to  be  in  some  cases 
considerable  damage  to  the  vitality  of  the  tree.  This  may  come  about 
through  an  interference  with  photosynthesis,  caused  by  the  light  being 
cut  off  through  the  layer  of  dust  upon  the  leaves  and  resulting  in  injury 
to  the  nutrition  of  the  tree,  although  this  fact  has  not  been  clearly 
established.  There  is  nothing  in  the  dust  itself  which  would  be  chem- 
ically injurious  to  the  tree  or  soil.  Question  has  also  been  raised  as  to  the 
effect  of  such  dust  deposition  upon  pollination  and  the  setting  of  fruit. 
"With  citrus  fruit  it  is  well  to  bear  in  mind  that  damage  of  this  sort  is 
very  doubtful  in  many  cases,  since  in  our  most  popular  variety  of  orange, 
the  Washington  Navel,  and  to  some  extent  in  other  citrus  fruits,  pollina- 
tion is  not  necessary,  and  does  not  ordinarily  occur,  the  fruit  developing 
by  vegetative  growth.  The  same  condition  exists  to  a  greater  or  less 
extent  in  other  citrus  fruits  which  have  a  tendency  toward  seedlessness. 


Bulletin  218]  CALIFORNIA  PLANT  DISEASES.  1061 

SOIL  INFLUENCES. 

Deficiencies. — We  have  shown  before  that  the  plant  requires  from  the 
soil  certain  specific  chemical  elements  in  proper  amounts  and  propor- 
tions, together  with  a  large  amount  of  water.  The  plant  differs  from 
the  animal  body  in  that  it  may  continue  growing  in  size  throughout  its 
Avhole  life  rather  than  ceasing  to  increase  at  a  certain  stage  of  maturity. 
The  amount  or  rapidity  of  this  increase,  if  temperature  conditions  are 
favorable  and  no  injurious  influences  present,  depends  almost  entirely 
upon  the  amount  of  the  necessary  elements  and  the  supply  of  water 
which  is  available  in  the  soil.  Particularly  noteworthy  in  this  connec- 
tion is  the  fact  that  the  lack  of  one  element  may  keep  back  the  whole 
development  of  the  plant,  even  though  all  the  others  are  present  and 
abundant.  On  this  account  the  whole  matter  of  successful  soil  fertiliza- 
tion depends  almost  entirely  upon  the  determination  of  the  limiting 
element  or  elements  and  applying  these  in  sufficient  quantities  for  maxi- 
mum results,  without  at  the  same  time  using  quantities  or  elements 
which  are  wasteful  and  without  effect. 

In  this  connection  the  function  of  water  and  the  possibility  of  its 
being  the  limiting  factor,  rather  than  any  chemical  element,  can  not  be 
too  strongly  emphasized.  There  is  no  question  that  in  a  large  portion 
of  the  citrus  acreage  of  California,  for  instance,  where  artificial  fertil- 
izers are  applied  more  or  less  regularly  and  in  fairly  large  amounts,  the 
deficiency  of  water  is  greater  than  that  of  any  chemical  element  and  a 
large  portion  of  the  fertilizers  applied  remains  inert  in  the  soil  or  is 
washed  away  by  rain  without  ever  reaching  the  interior  of  the  tree.* 
For  this  reason  it  is  extremely  important  in  the  examination  of  unthrifty 
trees  to  inquire  carefully  into  the  irrigation  treatment  which  the  trees 
have  received,  and?  much  more  important,  to  examine  the  soil  to  a  depth 
of  several  feet  and  find  out  positively  the  moisture  condition  of  the  lower 
layers  of  soil.     This  is  discussed  more  particularly  in  a  later  paragraph. 

We  would  not  infer  by  this  that  soils  are  never  deficient  in  chemical 
elements,  or  that  fertilization  is  never  effective.  Many  soils  are  decid- 
edly deficient  in  one  or  more  of  the  essential  elements,  and  practically  all 


*  In  order  to  give  further  weight  to  this  point  we  append  the  following  quotation  : 
"From  a  theoretical  point  of  view  it  is  not  possible  to  say  that  any  one  of  the 
main  soil  constituents  is  more  important  than  any  other,  since  all  are  necessary  to  a 
proper  functioning.  Practically,  however,  there  can  be  no  two  opinions  as  to  the 
supreme  importance  of  the  soil  water.  Nine  times  out  of  ten  it  is  the  supply  of  this 
constituent  which  limits  crop  production.  Usually  the  other  constituents  are  suffi- 
ciently if  not  maximally,  favorable,  and  poor  water  supply  and  infertility  go  hand 
in  hand.  Controlled  water  usually  means  controlled  fertility.  The  soil  water  must 
occupy,  then,  a  very  prominent  place  in  the  theories  of  the  soil  physicist,  and  the 
study  of  its  nature  and  movements  must  ever  be  a  most  important  and  absorbing 
branch  of  his  activity.  Nor  is  the  importance  of  the  soil  water  intrinsic  only.  It  is 
the  medium  of  the  soil  solution  and  only  through  it  are  the  necessary  food  elements 
carried  from  soil  to  plant.  From  soil  chemist,  as  from  soil  physicist,  the  soil  water 
is  receiving  ever  increased  attention  and  especially  so  in  the  light  of  the  most  modern 
theories  of  the  dynamics  of  plant  food." — E.  E.  Price,  "Studies  in  Soil  Physics  II" 
The  Plant  World,  Vol.  U,  page  59. 


1062  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION. 

soils,  after  continuous  cultivation  for  several  years,  become  exhausted. 
Moreover,  there  are  many  cases  of  soils  where  thrifty  plants  and  profit- 
able crops  can  still  be  grown  without  fertilization,  and  yet,  by  such 
practice,  an  increased  crop  can  be  obtained  which  will  prove  a  profitable 
investment  on  the  cost  of  fertilization. 

The  effects  of  a  deficiency  of  any  of  the  elements  most  commonly  lack- 
ing in  soils,  nitrogen,  phosphoric  acid  or  potash,  are  seen  as  a  backward- 
ness in  the  development  of  the  plant.  Nitrogen  is  most  noticeable  in  its 
effect  upon  growth,  and  is  most  likely  to  be  lacking  in  California  soils, 
yet  an  actual  deficiency  of  any  of  the  other  necessary  elements  is  equally 
effective  in  checking  development.  The  specific  effects  of  the  various 
elements  upon  plant  life  are  frequently  described,  but  we  have  little 
definite  information  of  this  sort  as  applied  to  California  crops.  With 
the  orange,  for  instance,  we  are  frequently  told  that  nitrogen  promotes 
especially  the  growth  of  the  tree;  that  phosphorus  is  most  concerned 
in  the  setting  of  the  fruit,  and  that  the  application  of  potash  produces 
more  sugar  in  the  fruit.  Various  statements  are  also  frequently  made 
as  to  the  effect  of  these  various  elements  upon  the  fruit  in  its  time 
of  maturity,  its  flavor,  texture,  color,  and  various  other  characteristics. 
"We  are  also  told  that  lack  of  iron  has  a  marked  influence  in  causing 
yellow,  light-colored  foliage,  and  that  an  application  of  this  element 
will  remedy  such  a  condition.  In  regard  to  these  ideas,  however,  we 
may  say  that  certainly  most  of  them  have  never  been  definitely  proven 
in  California.  The  most  careful  experiments  have  almost  entirely 
failed  to  show  any  specific  effects  or  differences  of  this  sort.  So  many 
other  influences  come  in,  such  as  those  of  temperature  and  other  cli- 
matic conditions,  soil  moisture,  variation  in  trees  and  other  compli- 
cated factors,  that  it  is  very  easy  to  ascribe  marked  differences,  noticeable 
in  a  single  season,  to  some  substance  which  has  been  applied  to  the  soil, 
when  really  some  other  influence  altogether  was  responsible  for  the  effect 
observed.  The  best  evidence  goes  to  show  that  any  fertilizing  element 
or  any  other  influence  which  promotes  the  growth  of  the  citrus  tree  like- 
wise promotes  and  increases  the  production  of  fruit.  It  also  appears 
to  be  a  fact  that  citrus  trees  which  are  best  nourished  and  in  the  most 
thrifty  condition  bear  the  best  fruit,  and  are  in  every  way  most  profit- 
able. 

The  specific  subject  of  the  methods  and  materials  of  soil  fertilization 
is  too  extensive  a  one  for  complete  consideration  here.  Persons  desiring 
information  along  this  line  should  consult  some  of  the  numerous  pub- 
lications upon  the  subject. 

We  may  say,  in  brief,  that  the  substances  mentioned  as  being  most 
likely  to  be  needed,  nitrogen,  phosphorus,  and  potash,  are  commonly 
supplied  either  in  the  form  of  stable  manure  or  in  various  substances, 
the  preparation  of  which  forms  a  large  and  important  industry.     Nitro- 


Bulletin  218]  CALIFORNIA  PLANT  DISEASES.  1063 

gen  is  supplied  in  the  form  of  salts,  such  as  nitrate  of  soda  and  sulphate 
of  ammonia,  or  in  various  substances  prepared  from  slaughterhouse 
refuse,  such  as  bone,  dried  blood,  and  tankage.  Phosphorus  comes  com- 
monly either  from  finely  ground  mineral  phosphates,  which  are  usually 
treated  with  sulphuric  acid  to  make  them  more  soluble  and  are  then 
called  superphosphate,  or  in  the  form  of  bone  or  other  animal  refuse. 
Potash,  as  used  in  California,  comes  almost  exclusively  from  the  salt 
sulphate  of  potash,  which  is  mined  in  Germany.  The  various  fertilizer 
dealers  supply  these  different  materials  and  are  also  in  the  habit  of  mix- 
ing them  together  in  supposedly  proper  proportions  into  so-called  com- 
plete fertilizers,  which  are  easier  and,  for  the  inexperienced,  sometimes 
safer  to  use. 

Deficiencies  in  nitrogen  in  the  soil  are  also  supplied  in  many  cases 
very  satisfactorily  and  economically  by  growing  and  plowing  under 
so-called  green  manure  or  cover  crops.  For  this  purpose  are  used 
certain  plants,  such  as  clover,  vetch,  peas  or  other  legumes,  which  have 
the  power  of  absorbing  nitrogen  from  the  air.  By  adding  large  amounts 
of  such  material  to  the  soil  its  stock  of  nitrogen  is  appreciably  increased 
and  its  mechanical  condition  likewise  improved. 

Excesses. — Plant  troubles  due  to  an  excess  of  certain  substances  in  the 
soil  are  very  frequently  met  with  in  California.  This  is  particularly 
the  case  in  so-called  alkali  soils.  In  such  cases  the  soil  is  impregnated 
with  excessive  and  harmful  amounts  of  certain  salts  which  in  more 
humid  climates  are  dissolved  by  the  frequent  rains  and  carried  away 
in  the  drainage. 

Alkali  Soils. — The  most  common  of  the  alkali  salts  are  the  so-called 
white  alkali,  sodium  sulphate,  and  black  alkali,  sodium  carbonate. 
Another  substance  frequently  found  in  soils  in  injurious  amounts  is 
common  salt,  sodium  chloride.  The  presence  of  these  salts  is  not  usually 
difficult  of  detection  in  a  superficial  examination,  while  by  chemical 
analysis  their  presence  and  amount  can  be  absolutely  determined. 
Alkali  lands  are  usually  characterized  by  spots  or  areas  of  greater  or 
less  extent  where  a  white  incrustation  can  be  seen  upon  the  surface  of 
the  ground.  Black  alkali  is  so  called  from  the  fact  that  when  wet 
it  dissolves  the  humus  of  the  soil,  forming  a  black,  greasy  looking  sub- 
stance upon  the  surface  of  the  soil,  or  giving  a  black  color  to  surface 
water.  The  effect  upon  native  vegetation  is  always  quite  characteristic 
of  the  presence  and  amount  of  alkali  salts.  Certain  species  of  plants 
prefer  alkali  soil  and  flourish  according  to  the  amount  of  these  sub- 
stances which  the  soil  contains.  Most  plants,  however,  are  easily 
injured  by  them,  with  the  result  that  spots  containing  any  considerable 
amount  of  these  injurious  salts  either  have  upon  them  the  above  men- 
tioned characteristic  plants  or  remain  bare  of  vegetation  with  the  alkali 


1064  UNIVERSITY   OF    CALIFORNIA EXPERIMENT   STATION. 

crust  upon  the  surface,  while  the  surrounding  ground  is  covered  with 
normal  vegetation.  In  every  case  where  there  is  any  reason  to  suspect 
the  effects  of  alkali  or  other  injurious  salts,  the  soil  should  be  chemically 
analyzed  down  to  a  depth  of  several  feet. 

The  present  subject,  although  belonging  more  in  the  field  of  the  soil 
chemist  than  that  of  the  plant  pathologist,  is  of  so  much  importance  in 
the  study  of  plant  diseases  in  California  that  we  have  thought  it  desir- 
able in  this  chapter  to  make  the  following  quotations  from  Professor 
E.  W.  Hilgard's  authoritative  treatment  of  the  subject:* 

Effects  of  Alkali  Upon  Culture  Plants. — In  land  very  strongly  impregnated  with 
alkali  salts,  most  culture  plants,  if  their  seed  germinates  at  all,  will  show  a  sickly 
growth  for  a  short  time,  "spindle  up"  and  then  die  without  fruiting.  In  soils  less 
heavily  charged  the  plants  may  simply  become  dwarfed,  and  fruit  scantily.  The 
effect  on  grown  trees  around  which  alkali  has  come  up,  is  first,  scanty  leafage  and 
short  growth  of  shoots,  themselves  but  sparsely  clothed  with  leaves. 

Nature  of  the  Injury  to  Plants  from  Alkali. — When  we  examine  plants  that  have 
been  injured  by  alkali,  we  will  mostly  find  that  the  visible  damage  has  been  done 
near  the  base  of  the  trunk,  or  root  crown;  rarely  at  any  considerable  depth  in  the 
soil  itself.  In  the  case  of  green  herbaceous  stems,  the  bark  is  found  to  have  been 
turned  to  a  brownish  tinge  for  half  an  inch  or  more,  so  as  to  be  soft  and  easily  peeled 
off.  In  the  case  of  trees,  the  rough  bark  is  found  to  be  of  a  dark,  almost  blackr 
tint,  and  the  green  layer  underneath  has,  as  in  the  case  of  herbaceous  stems,  been 
turned  brown  to  a  greater  or  less  extent.  In  either  case  the  plant  has  been  practi- 
cally "girdled,"  the  effect  being  aggravated  by  the  diseased  sap  poisoning  more  or 
less  the  whole  stem  and  roots.  The  plant  may  not  die,  but  it  will  be  quite  certain  to 
become  unprofitable  to  the  grower. 

It  is  mainly  in  the  case  of  land  very  heavily  charged  with  common  salt,  as  in  the 
marshes  bordering  the  sea,  or  salt  lakes,  that  injury  arises  from  the  direct  effects 
of  the  salty  soil-water  upon  the  feeding  roots  themselves.  In  a  few  cases  the 
gradual  rise  of  salt  water  from  below,  in  consequence  of  defective  drainage,  has 
seriously  injured,  and  even  destroyed,  old  orange  orchards.  The  natural  occupancy 
of  the  ground  by  certain  native  plants  may  be  held  to  indicate  that  the  soil  is  too 
heavily  charged  with  saline  ingredients  to  permit  healthy  root  growth  or  nutrition 
until  the  excess  of  salts  is  removed. 

The  fact  that  in  cultivated  land  the  injury  is  usually  found  to  occur  near  the 
surface  of  the  soil,  concurrently  with  the  well-known  fact  that  the  maximum  accu- 
mulation of  salts  at  the  surface  is  always  found  near  the  end  of  the  dry  season, 
indicates  clearly  that  this  accumulation  is  due  to  evaporation  at  the  surface.  The 
latter  is  often  found  covered  with  a  crust  consisting  of  earth  cemented  by  the  crystal- 
lized salts  and  later  in  the  season  with  a  layer  of  whitish  dust  resulting  from  the 
drying-out  of  the  crust  first  formed.  It  is  this  dust  which  becomes  so  annoying  to 
the  inhabitants  and  travelers  in  alkali  regions,  when  high  winds  prevail,  irritating 
the  eyes  and  nostrils  and  parching  the  lips. 

Effects  of  Irrigation. — One  of  the  most  annoying  and  discouraging  features  of  the 
cultivation  of  lands  in  alkali  regions  is  that,  although  in  their  natural  condition 
they  may  show  but  little  alkali  on  their  surface,  and  that  mostly  in  limited  spots, 
these  spots  are  found  to  enlarge  rapidly  as  irrigation  is  practiced.  Yet  since  alkali 
salts  are  the  symptoms  and  result  of  insufficient  rainfall,  irrigation  is  a  necessary 
condition  of  agriculture  wherever  they  prevail.  Under  irrigation,  neighboring  spots 
will  oftentimes  merge  together  into  one  large  one,  and  at  times  the  entire  area,  once 
highly  productive  and  perhaps  covered  with  valuable  plantations  of  trees  or  vines, 
will  become  incapable  of  supporting  useful  growth.     This  annoying  phenomenon  is 


*"Soils,"  pages  426-429. 


Bulletin  218]  CALIFORNIA  PLANT  DISEASES.  1065 

popularly  known  as  "the  rise  of  the  alkali"   in   the  western   United   States,   but  is 
equally  well  known  in  India  and  other  irrigation  regions. 

The  soil  being  impregnated  with  a  solution  of  the  alkali  salts,  and  acting  like  a 
wick,  the  salts  naturally  remain  behind  on  the  surface  as  the  water  evaporates,  the 
process  only  stopping  when  the  moisture  in  the  soil  is  exhausted.  We  thus  not 
infrequently  find  that  after  an  unusually  heavy  rainfall  there  follows  a  heavier 
accumulation  of  alkali  salts  at  the  surface,  while  a  right  shower  produces  no  per- 
ceptible permanent  effect.  We  are  thus  taught  that,  within  certain  limits,  the  more 
water  evaporates  during  the  season  the  heavier  will  be  the  rise  of  the  alkali ;  pro- 
vided that  the  water  is  not  so  abundant  as  to  leach  the  salts  through  the  soil  and 
sub-soil  into  the  subdrainage. 

Leaky  Irrigation  Ditches. — Worst  of  all,  however,  is  the  effect  of  irrigation  ditches 
laid  in  sandy  lands  (such  as  are  naturally  predominant  in  arid  regions)  without 
proper  provision  against  seepage.  The  ditch  water  then  gradually  fills  up  the  entire 
substrata  so  far  as  they  are  permeable,  and  the  water-table  rises  from  below  until 
it  reaches  nearly  to  the  ditch  level,  shallowing  the  subsoil,  drowning  out  the  deep 
roots  of  all  vegetation,  and  bringing  close  to  the  surface  the  entire  mass  of  alkali 
salts  previously  diffused  through  many  feet  of  substrata. 

An  effect  similar  to  that  described  in  the  last  paragraph  is  sometimes 
seen  in  the  case  of  young  seedlings,  as  in  seed  beds  of  eucalyptus  or 
orange  trees,  grown  in  soil  containing  a  considerable  amount  of  alkali  or 
salt,  especially  if  they  are  watered  with  water  of  a  similar  nature.  In 
such  cases  the  young  plants  frequently  begin  dying  in  a  manner  very 
similar  to  that  produced  by  damping-off  fungi.  The  natural  tendency 
for  the  grower  is  then  to  use  less  water  and  endeavor  to  keep  the  soil  as 
dry  as  possible,  which  in  the  present  case  has  the  effect  of  increasing 
rather  than  preventing  the  injury,  since  the  injurious  salts  tend  to 
accumulate  by  evaporation  about  the  stem  of  each  seedling.  As  to  the 
best  method  of  procedure  in  such  cases,  assuming  that  the  trouble  is 
known  to  be  due  to  injurious  salts  and  not  a  case  of  true  damping-off 
caused  by  the  fungi,  we  may  again  quote  from  Hilgard  (p.  249)  : 

Mode  of  Using  Saline  Irrigation  Waters. — The  fact  that  abundant  growth  of 
native  as  well  as  cultivated  plants  may  sometimes  be  seen  on  the  margins  of  "alkali 
lakes"  where  water  of  over  a  hundred  grains  of  mineral  salts  per  gallon  continuously 
bathes  the  roots,  while  the  same  plants  perish  at  some  distance  from  the  water's 
edge,  points  the  way  to  the  utilization,  in  emergencies,  of  fairly  strong  saline  waters, 
viz.,  by  the  prevention  of  their  concentration  to  the  point  of  injury  by  evaporation. 
It  is  clear  that  when  such  waters  are  used  sparingly,  so  as  to  penetrate  but  a  few 
feet  underground,  whence  the  moisture  re-ascends  for  evaporation  at  the  surface,  a 
few  repetitions  of  its  use  will  accumulate  so  much  alkali  near  the  surface  as  to  bring 
about  serious  injury.  If,  on  the  other  hand,  the  water  is  used  so  abundantly  that 
the  roots  may  be  considered  as  being,  like  the  marginal  vegetation  of  alkali  lakes, 
bathed  only  by  water  of  moderate  strength,  no  such  injury  need  occur ;  and  what 
does  accumulate  in  consequence  of  the  inevitable  measure  of  evaporation  occurring 
in  the  course  of  a  season,  may  be  washed  out  of  the  land  by  copious  winter  irrigation. 

This,  of  course,  presupposes  that  the  land,  as  is  mostly  the  case  in  the  arid 
region,  is  readily  drained  downwards  when  a  sufficiency  of  water  is  used.  When 
this  is  not  the  case,  e.  g.,  in  clay  or  adobe  soils,  or  in  those  underlaid  by  hardpan, 
waters  which  in  sandy  land  could  have  been  used  with  impunity,  may  become  inap- 
plicable to  irrigation  use. 

Apparent  Paradox. — Tne  prescription  to  use  saline  waters  more  abundantly  than 
purer  ones,  in  order  to  avoid  injury  from  alkali,  though  paradoxical  at  first  sight,  is 


1066  UNIVERSITY   OF    CALIFORNIA — EXPERIMENT    STATION. 

therefore  plainly  justified  by  common  sense  as  well  as  by  experience,  in  pervious 
(sandy)  soils;  while  in  difficultly  permeable  ones,  their  use  may  be  either  wholly 
impracticable,  or  subject  to  very  close  limitation. 

Sometimes  the  alternate  use  of  pure  and  salt-charged  water  serves  to  eke  out  a 
too  scant  supply  of  the  former.  But  in  all  such  cases,  close  attention  to  the  measure 
of  water  that  will  wet  the  soil  to  a  certain  depth,  and  "eternal  vigilance"  with 
respect  to  the  accumulation  of  alkali  near  the  surface,  must  be  the  price  of  immunity 
from  injury.  In  all  cases  the  farmer  should  know  how  much  of  alkali  salt  he 
introduces  into  the  land  with  the  irrigation  water,  and  watch  that  it  does  not 
approach  too  closely,  or  exceed,  the  tolerance  of  his  crops  for  alkali  salts. 

A  proper  discussion  of  the  methods  of  utilization  and  improvement 
of  alkali  lands  would  be  too  extensive  to  include  in  a  publication  of  this 
sort.  The  subject  is  very  fully  treated  by  Hilgard,  pages  422  to  484. 
We  may  say,  in  a  general  way,  that  the  possibilities  in  this  direction  lie, 
first  in  the  planting  of  crops  most  resistant  to  such  conditions,  since 
cultivated  plants  vary  widely  in  this  respect.  The  date  palm,  for 
instance,  grows  and  flourishes  in  soil  where  almost  no  other  cultivated 
plant  can  maintain  its  existence.  The  grapevine  and  olive  are  also 
highly  resistant,  while  the  peach,  apricot,  and  prune  are  much  more 
sensitive.  The  specific  substance  present  in  the  soil,  whether  sodium 
carbonate  (black  alkali),  sodium  sulphate  (white  alkali),  or  sodium 
chloride  (common  salt),  is  of  great  importance  in  this  connection,  as 
the  relative  tolerance  of  various  plants  for  these  different  salts  varies 
widely.  It  is  also  to  be  remembered  that  in  the  case  of  fruit  trees 
there  is  usually  some  choice  in  regard  to  the  kind  of  root  upon  which 
the  trees  may  be  budded  or  grafted,  as  the  various  roots  vary  consid- 
erably in  their  tolerance  of  saline  salts. 

In  addition  to  the  possibilities  of  utilizing  alkali  lands  by  the  choice 
of  resistant  plants,  the  possibilities  of  reclaiming  or  improving  such 
lands  lie  mostly  in  the  direction  of  dissolving  out  the  injurious  salts 
by  flooding  with  water,  and  then  removing  the  water  with  the  salts  in 
solution  by  drainage.  Much  good  may  be  done  in  this  manner  where 
an  abundant  supply  of  fairly  pure  water  is  available  and  the  topography 
of  the  land  is  such  that  drainage  can  be  secured.  Something  can  also 
be  done  in  the  way  of  neutralizing  or  changing  the  composition  of  these 
soils  by  application  of  chemical  substances  to  the  soil.  It  has  been 
demonstrated,  for  instance,  that  in  the  case  of  black  alkali  (sodium 
carbonate),  a  change  of  this  substance  to  white  alkali  (sodium  sulphate), 
can  be  effected  by  an  application  of  gypsum,  the  sulphate  being  much 
less  injurious  to  vegetation  than  the  carbonate.  This  whole  subject  is 
discussed  at  length  by  Hilgard. 

Acid  Soils. — Vegetation  is  sometimes  injured  or  its  growth  prevented 
by  an  acid  or  sour  condition  of  the  soil.  This  is  much  less  common  in 
California,  however,  than  in  the  Atlantic  States.  It  is  more  apt  to  occur 
in  wet,  swampy  land,  or  in  recently  cleared  forest  soils,  where  there  is 


Bulletin  218]  CALIFORNIA  PLANT  DISEASES.  1067 

a  large  amount  of  vegetable  matter  in  the  ground.     Such  a  condition 
can  be  definitely  determined  by  chemical  analysis. 

Soil  acidity  is  corrected  by  the  application  of  lime.  (See  Hilgard, 
pages  122  and  123.) 

EFFECTS  OF  DRYNESS. 

(The  following  discussion  presupposes  to  a  large  extent  the  avail- 
ability of  water  for  irrigation  purposes,  yet  it  is  to  be  remembered  that 
large  areas  of  fruit  tree  and  other  crops  are  grown  in  California  without 
irrigation.  What  is  said  in  regard  to  the  use  of  irrigation  water  will, 
of  course,  not  apply  in  such  cases.  The  grower  of  non-irrigated  crops 
must  look  to  choice  of  soil  and  location  and  cultural  methods  of  moisture 
conservation.  What  is  said  in  regard  to  physical  soil  defects  as  affecting 
the  moisture  supply  applies  even  more  forcibly  in  this  case  than  in  that 
where  irrigation  is  practiced.) 

Some  of  the  greatest  mistakes  in  California  horticulture  have  been 
made  in  the  attempt  to  grow  crops,  particularly  tree  fruits,  without 
irrigation.  Many  acres  of  dying  or  dead,  abandoned  orchards  still 
remain  to  testify  to  the  disastrous  results  of  such  experiments.  Further- 
more, it  may  be  said  that  even  in  the  case  of  a  large  acreage  of  orchard 
fruits  which  is  still  being  cultivated  and  producing  fairly  profitable 
returns,  such  returns  would  be  very  much  greater  if  water  for  irriga- 
tion were  available.  Even  in  cases  where  irrigation  might  not  be  neces- 
sary every  year,  a  possible  source  of  water  supply  to  be  drawn  upon 
during  dry  years  would  be  the  most  valuable  form  of  insurance  which 
the  grower  could  obtain.  There  are  many  orchards  and  large  areas  of 
land  in  California  where  good  returns  are  obtained  year  after  year 
without  irrigation,  yet  even  in  the  most  favorable  cases  as  the  trees 
grow  older,  filling  the  soil  with  roots,  drawing  more  completely  upon 
its  moisture  content,  and  demanding  more  and  more  water  as  the  tops 
grow  larger  and  the  crops  greater,  the  desirability  of  irrigation  is  likely 
to  become  more  or  less  pronounced.  Nothing  should  be  considered  more 
seriously  by  the  intending  planter  than  the  water  question,  and  he 
should  undertake  planting  without  the  possibility  of  irrigation  only 
with  the  utmost  conservatism. 

No  doubt  more  trouble  and  failure  in  cultivated  plants  is  caused  in 
California  from  lack  of  soil  moisture  than  from  any  other  influence. 
While  it  would  seem  that  so  simple  a  cause  would  be  readily  seen  and 
remedied,  yet  it  is  a  fact  that  under  our  semi-arid  conditions,  where 
irrigation  during  most  of  the  growing  season  is  usually  an  absolute 
necessity,  a  lack  of  a  sufficient  amount  of  water  quite  unsuspected  by 
the  grower  is  one  of  our  most  common  troubles.  It  is  due  in  some  cases 
to  an  insufficient  supply  of  available  water,  making  it  impossible  to 
obtain  the  necessary  amount,  but  more  often  to  a  failure  of  the  grower 


1068  UNIVERSITY   OF    CALIFORNIA — EXPERIMENT    STATION. 

to  realize  or  examine  the  condition  of  the  soil  beneath  the  surface,  and 
a  failure  to  apply  the  necessary  amount  of  moisture  or  to  use  methods 
which  would  insure  its  absorption  by  the  deeper  layers  of  soil.  In  our 
citrus  groves,  for  instance,  no  experience  is  more  common  in  examining 
trees  supposed  to  be  suffering  from  some  mysterious  disease,  than  to  dig 
down  three  or  four  feet  or  less  below  the  surface  and  find  the  soil 
entirely  dry,  much  to  the  surprise  of  the  owner.  Sometimes,  also,  in  the 
case  of  deciduous  as  well  as  citrus  groves,  in  the  winter  when  rainfall 
is  commonly  expected  to  provide  sufficient  moisture,  the  subsoil  may  be 
found  extremely  dry  because  the  usual  amount  of  rain  has  not  occurred. 
Trees  often  suffer  severely  from  this  cause,  even  when  in  a  dormant 
condition.  Particularly  in  the  fall,  after  the  crop  and  leaves  are  off, 
deciduous  orchards  often  go  for  many  weeks  without  rain  or  irrigation, 
the  grower  failing  to  realize  that  the  trees  need  a  plentiful  supply  of 
water  even  though  they  are  not  growing  or  carrying  a  crop  of  fruit. 
Severe  injury  is  frequently  caused  in  this  manner  to  walnut,  apple,  and 
other  similar  trees,  which  injury  shows  itself  in  a  poor  crop  or  die-back 
condition  the  following  season. 

In  citrus  groves  the  uncertainties  of  our  rainy  season  lead  often  to 
equally  bad  results.  The  usual  practice  in  citrus  irrigation  consists  in 
an  application  of  water  about  every  thirty  days,  on  the  average,  during 
the  dry  summer  season,  which  application  is  supposed  to  be  supple- 
mented by  copious  rainfall  during  the  winter  months.  Such  rainfall 
is  expected  to  soak  the  ground  more  completely  and  deeply  than  can 
ordinarily  be  accomplished  by  irrigation,  and  is  counted  upon  partic- 
ularly to  create  a  subterranean  store  of  moisture  in  the  subsoil.  The 
citrus  grower  expects,  in  an  average  season,  sufficient  rainfall  to  make 
irrigation  unnecessary  during  a  period  extending  from  about  November 
first  to  May  first.  Relying  upon  such  an  expectation  his  tendency  is 
to  withhold  irrigation  after  October,  waiting  for  the  expected  rain,  and 
to  put  it  off  as  late  as  possible  in  the  spring  for  the  same  reason.  The 
grower  of  deciduous  fruits,  whose  crop  comes  off  in  the  summer  and 
whose  trees  are  leafless  and  dormant  during  the  winter,  stops  irrigating 
still  earlier  and  is  apt  to  pay  little  attention  to  his  trees  after  the  crop 
is  gathered. 

Most  seasons  this  confidence  in  the  elements  is  not  misplaced,  rain 
coming  soon  enough  and  late  enough  to  prevent  serious  damage.  From 
time  to  time,  however,  a  season  occurs  when  the  rain  does  not  come  on 
schedule  time  in  the  fall,  or  the  rainy  season  ceases  unusually  early  in 
the  spring.  In  such  seasons  the  grower,  with  each  day's  waiting,  is 
more  and  more  certain  that  rain  will  come  and  continues  to  postpone 
irrigation.  Serious  injury  is  sometimes  caused  in  this  way  and  one 
which  may  lead  to  more  obscure  after-effects,  such  as  die-back,  gumming, 


Bulletin  218]  CALIFORNIA  PLANT  DISEASES.  1069 

mottled  leaf,  and  other  pathological  symptoms.  Particularly  when  a 
dry  fall  follows  a  dry  spring,  making  nearly  a  year  without  rain,  is 
this  sort  of  trouble  likely  to  occur.  In  such  a  season,  even  with  more 
irrigation  than  usual,  the  soil  does  not  get  the  deep  soaking  which  only 
long,  heavy  rains  can  give  it,  and  the  subsoil  is  likely  to  dry  out.  This 
condition  is  most  pronounced,  naturally,  on  soils  underlaid  with  a  porous 
subsoil  not  having  the  greatest  water-retaining  capacity,  or  where  there 
is  hardpan  or  other  hard  material  beneath  the  surface,  preventing  a 
deep  soaking-in  of  the  water.  The  average  irrigation  comes  far  from 
equalling  a  good  rain  in  wetting  the  ground.  "When  the  winter  rain  is 
up  to  or  above  the  average  in  amount  and  distributed  over  its  normal 
season,  groves  which  receive  even  tolerable  irrigation,  upon  soil  of  even 
moderate  water-retaining  properties,  may  go  through  in  fairly  good 
condition.  Following  the  dry  seasons  the  groves  where  the  subsoil 
dried  out  begin  to  show  up  and  exhibit  signs  of  distress.  In  the  very 
driest  years  this  may  extend  to  groves  upon  soil  which  ordinarily  is 
considered  to  have  good  water-retaining  qualities. 

The  effect  of  frost  and  cold  weather  is  much  more  decided  on  trees  in 
this  dry  condition  than  upon  those  which  have  their  tissue  filled  with  the 
proper  amount  of  moisture,  and  numerous  instances  are  to  be  seen  of 
severe  frost  injury  to  citrus  and  deciduous  trees  in  groves  allowed  to 
become  extremely  dry  in  the  fall,  while  neighboring  groves,  which 
receive  proper  irrigation,  are  entirely  unaffected. 

A  dry  condition  of  the  subsoil  is  frequently  brought  about,  even 
where  the  amount  of  water  available  is  sufficient,  through  faulty  physical 
conditions  such  as  hardpan,  soils  underlaid  with  rock  close  to  the 
surface,  sandy  or  gravelly  subsoil,  or  other  similar  conditions  which 
prevent  the  retention  of  a  proper  amount  of  moisture  several  feet  below 
the  surface  of  the  ground.  All  sorts  of  conditions  may  occur  which 
have  this  effect  of  limiting  the  moisture  supply  available  to  the  roots, 
and,  as  we  have  just  said,  nothing  is  more  common  in  California  than 
to  find  plant  troubles  due  to  this  cause.  This  is  one  of  the  most  impor- 
tant reasons,  therefore,  for  digging  down  into  the  soil  to  an  ample  depth 
in  investigating  cases  of  failure  or  poor  development. 

In  some  parts  of  the  State,  particularly  in  the  northern  portion,  a 
very  irregular  soil  moisture  condition  occurs,  due  to  the  combination  of 
a  heavy  winter  rainfall  and  a  very  dry,  hot  summer,  with  a  porous, 
gravelly  soil  more  or  less  underlaid  by  hardpan.  In  such  regions  the 
soil  becomes  extremely  wet  in  winter  and  if  hardpan  exists  near  the 
surface  the  water  does  not  drain  away  but  the  soil  remains  saturated 
clear  to  the  surface.  After  the  rains  cease,  however,  the  moisture  dries 
out  rapidly,  so  that  during  the  summer  the  dryness  of  the  soil  reaches 
an  equally  extreme  stage.     Large  areas  of  orchard  have  been  planted 

3— Bul.  218 


1070  UNIVERSITY   OF    CALIFORNIA EXPERIMENT    STATION. 

under  conditions  similar  to  this  without  irrigation  under  the  impression 
that  no  irrigation  would  be  needed,  on  account  of  the  large  amount  of 
rainfall  and  the  extremely  wet  condition  of  the  soil  during  the  winter. 
Such  plantings,  however,  have  in  every  case  resulted  in  absolute  failure, 
except  where  subsequently  a  permanent  water  supply  for  irrigation  was 
secured.  The  trees  linger  along  for  a  few  years,  making  a  fair  growth 
at  first,  but  ultimately  becoming  stunted,  affected  by  die-back,  and  finally 
dying  completely,  except  in  the  case  of  the  most  drouth-resistant  species. 

The  remedy  for  such  troubles  is  usually  obvious,  consisting  in  choos- 
ing, so  far  as  possible,  deep  soils  with  fairly  heavy  subsoil,  and  in 
obtaining  a  sufficient  water  supply,  using  methods  for  its  distribution 
and  application  which  will  insure  a  proper  moistening  of  the  soil  to  a 
sufficient  depth.  When  trouble  of  this  sort  is  once  realized  it  is  in  many 
cases  not  difficult  to  remedy  it  by  proper  cultural  methods,  if  the  soil  is 
of  proper  quality  and  particularly  if  sufficient  water  for  irrigation  is 
available.  Again  we  would  say,  however,  that  a  failure  to  examine  the 
subsoil  by  deep  digging  and  a  consequent  lack  of  knowledge  of  its 
moisture  condition  is  one  of  our  most  common  causes  of  tree  failure. 
Frequently,  even  at  the  very  time  of  irrigation,  when  the  surface  soil 
was  saturated  and  covered  with  water,  it  has  been  found  that  at  a  depth 
of  two  or  three  feet  the  ground  was  completely  dry  on  account  of  a  plow- 
sole  or  hardpan  which  prevented  the  water  from  soaking  down  to  a 
proper  depth.  It  will  be  seen  from  what  has  been  said  that  this  sort  of 
trouble  may  occur  from  one  of  two  causes :  either  from  a  too  porous  sub- 
soil with  insufficient  water-retaining  quality,  or  from  a  hard  layer 
beneath  the  surface  which  does  not  allow  the  proper  penetration  of 
water. 

The  methods  of  improving  these  conditions  are  considered  in  another 
chapter,  see  page  1074.  It  is  obvious  that  the  remedy  lies  on  the  one 
hand  in  adding  humus  or  organic  matter  to  the  lighter  soils  to  make  them 
hold  water  better,  and  on  the  other  hand  in  breaking  up  the  hard  layer  of 
subsoil  in  order  to  allow  the  water  to  penetrate  more  rapidly  and  deeply. 
Beyond  these  methods  of  soil  improvement  there  must  also  be  considered 
the  methods  of  irrigation  best  adapted  to  each  condition.  In  order  to 
keep  more  moisture  in  the  soil  there  are  three  possibilities  in  addition 
to  what  may  be  accomplished  by  cultural  means :  either  more  water  must 
be  put  on  at  the  usual  time  of  irrigation,  or  the  water  must  be  put  on 
more  frequently,  or  the  irrigation  season  must  begin  earlier  or  be  ex- 
tended later  to  connect  more  closely  with  the  rainy  season.  It  may,  for 
instance,  be  necessary  with  an  orchard  having  a  light,  porous  subsoil, 
especially  in  a  dry  season,  to  irrigate  oftener  than  every  thirty  days,  if 
the  water  can  be  obtained,  or  to  irrigate  earlier  or  later  in  the  season 
than  is  customary.     On  heavier  soils,  or  where  it  is  impossible  to  get 


Bulletin  218]  CALIFORNIA  PLANT  DISEASES.  1071 

water  other  than  at  the  regular  time,  it  may  be  possible  and  effective 
to  put  on  more  water  than  has  been  the  practice.  It  is  easier  and 
cheaper,  of  course,  to  put  on  larger  amounts  of  water  at  longer  intervals 
rather  than  smaller  amounts  at  shorter  intervals.  The  former  method  is 
also  more  likely  to  conform  with  the  established  regulations  in  most  irri- 
gation districts.  Such  considerations  and  the  water-retaining  capacity 
of  the  subsoil  must  govern  the  grower. 

In  addition  to  the  moistening  of  the  soil  by  irrigation,  there  must  not 
be  forgotten  the  possibilities  of  preventing  surface  evaporation  by  fre- 
quent cultivation.  This  leads  us,  however,  too  far  from  our  subject, 
and  we  must  leave  the  matter  with  this  suggestion.  Most  important  of 
all  is  for  the  grower  to  know  definitely  the  moisture  condition  of  the 
soil  at  all  times  down  to  a  depth  of  at  least  four  feet,  disregarding 
entirely  the  appearance  on  the  surface,  and  irrigate  accordingly. 

EFFECTS  OF  EXCESSIVE  MOISTURE. 

Although  a  lack  of  moisture  is  so  common  in  our  cultivated  soils,  yet 
cases  are  also  quite  common  and  sometimes  entirely  unsuspected  where 
there  is  too  much  water  in  the  subsoil,  and  vegetation  suffers  accordingly. 
This,  again,  can  be  easily  determined  by  digging  a  hole  down  to  the 
depths  of  the  lower  roots  and  examining  the  condition  of  the  soil  as  to 
moisture.  In  some  regions  the  natural  water  level  is  near  the  surface, 
and  this  fact  must  be  kept  in  mind  and  the  level  of  the  water  accurately 
determined  before  making  extensive  plantings.  Again,  through  irriga- 
tion or  otherwise,  the  water  level  may  be  raised,  either  in  the  hollows  and 
lower  spots  of  a  region  where  the  surface  is  uneven,  or  under  the  whole 
surface  of  large  areas  where  the  surface  is  level.  The  latter  case  has 
already  been  alluded  to  in  our  discussion  of  alkali  soils  and  the  rise  of 
water  in  the  same,  page  1064.  Many  large  areas  of  good  land  in  Cali- 
fornia have  been  rendered  almost  worthless  in  this  manner  and  often  this 
condition  has  come  about  and  orchards  and  other  plantings  been  severely 
injured  before  the  true  condition  was  realized  by  the  owner.  Here, 
again,  the  simple  process  of  digging  a  hole  to  a  depth  of  several  feet 
in  the  ground  is  sufficient  to  indicate  the  cause  of  the  trouble.  Trees 
affected  in  this  manner  usually  begin  dying  in  the  top  and  at  the  ends 
of  the  branches,  the  leaves  developing  poorly,  turning  yellow  and  falling 
off  as  the  die-back  proceeds.  The  effect  is  very  similar  to  that  produced 
by  dryness  of  the  soil,  and,  in  fact,  the  effect  upon  the  parts  above 
ground  is  practically  the  same  in  either  case.  If  the  soil  is  too  dry,  the 
top  suffers  because  the  roots  can  not  send  up  the  proper  amount  of 
moisture,  while  if  the  soil  is  too  wet  the  roots  are  injured  and  killed  and 
again  the  top  fails  to  receive  what  it  should  from  the  roots. 

One  of  the  worst  troubles  of  this  sort  is  experienced  in  cases  where  the 


1072  UNIVERSITY   OF    CALIFORNIA — EXPERIMENT   STATION. 

water  level  does  not  remain  constant,  either  high  or  low,  but  rises  and 
falls  a  considerable  number  of  feet  during  the  year.  This  is  a  condition 
of  quite  frequent  occurrence  in  some  sections,  particularly  in  the  vicinity 
of  large,  uncemented  irrigation  canals  in  sandy  soil.  In  such  places 
the  water  level  of  the  surrounding  country  may  come  up  nearly  to  the 
surface  of  the  ground  during  the  irrigation  season  when  the  canals  are 
constantly  full  of  water,  while  after  the  water  is  shut  off  its  level  in  the 
soil  goes  down  for  many  feet.  Under  such  conditions,  the  roots  have  no 
opportunity  to  accustom  themselves  to  development  at  a  certain  level, 
but  are  continually  subjected  to  alternate  flooding  and  drying.  Such  a 
condition  can  be  determined  by  digging  an  open  pit  or  well  to  a  depth 
of  10  or  15  feet,  and  watching  the  fluctuation  of  the  water  level  during 
the  season. 

The  only  remedy  for  all  these  conditions  consists  in  drainage  to  pre- 
vent the  water  rising  above  a  certain  level,  and,  in  the  last  instance 
described,  in  cementing  the  bottom  and  sides  of  the  main  ditches  so  that 
seepage  can  not  occur.  The  latter  is  expensive  but  is  the  only  means  of 
stopping  the  widespread  injury  of  this  sort,  which  is  at  present  occurring 
in  some  regions. 

EFFECTS  OF  FAULTY  PHYSICAL  STRUCTURE. 

Cultivated  plants  frequently  suffer  or  die  on  account  of  unfavorable 
conditions  of  structure  or  formation  of  the  subsoil.  Nothing  is  more 
fatal  to  the  success  of  the  land-seeker  in  California  than  to  judge  the 
value  of  a  piece  of  ground  by  the  nature  of  the  surface  soil.  By  digging 
or  boring  down  to  a  depth  of  a  few  inches  or  feet  he  may  encounter 
something  entirely  different  from  that  seen  on  top,  and  something  which 
would  doom  his  proposed  planting  to  absolute  failure  from  the  very 
start.  Again,  plantings  may  be  made  and  flourish  for  a  time,  but  then 
begin  to  fail  as  the  roots  reach  the  unfavorable  conditions  below. 

Faults  of  this  sort  are  most  commonly  of  two  general  classes,  namely, 
the  subsoil  is  either  too  hard  and  impenetrable,  preventing  the  roots 
from  developing  properly  and  limiting  the  supply  of  moisture  available 
for  them ;  or  it  is  too  coarse  and  porous,  being  unable  to  retain  moisture, 
and  deficient  in  plant  food.  In  the  former  instance,  on  digging  down 
into  the  soil  one  may  encounter  at  a  slight  depth  solid  rock,  hard  clay 
(hardpan),  or  he  may  come  into  gravel,  coarse  sand,  or  some  other 
undesirable  soil  formation.  Again,  in  the  case  of  old,  long  cultivated 
orchards,  particularly  in  heavy  soils,  an  artificial  hardpan  or  plow-sole  is 
frequently  formed  on  account  of  the  gathering  together  of  the  finest  soil 
particles  at  a  depth  just  below  that  reached  by  the  plow  and  cultivator. 
All  of  these  conditions  can  be  readily  determined  by  digging  or  boring 
down  into  soil. 

The  chief  difficulty  in  this  respect  is  that  of  judging  accurately  just 


Bulletin  218] 


CALIFORNIA   PLANT    DISEASES. 


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1074  UNIVERSITY   OF    CALIFORNIA — EXPERIMENT    STATION. 

what  degree  of  hardness  or  coarseness  in  the  subsoil  is  undesirable  or  in- 
jurious, or  what  conditions  in  these  respects  are  desirable  and  favorable 
to  plant  life.  On  the  one  hand,  the  heavier  the  soil  the  better  it  will 
retain  moisture  and  plant  food,  so  long  as  it  is  not  so  extremely  hard  or 
impervious  as  to  prevent  its  being  penetrated  by  roots  and  water.  On 
the  other  hand,  the  heavier  the  soil  the  more  difficult  it  is  to  cultivate, 
while  if  it  is  sandy  and  porous  it  is  easier  to  handle,  takes  up  water  more 
readily,  and  is  more  easily  penetrated  by  plant  roots.  On  lighter  soils 
plants  usually  respond  more  promptly  to  applications  of  water  and 
plant  food ;  such  soils  are  easier  to  plow  and  cultivate  and  can  be  worked 
at  any  time  of  year,  while  heavy  soils  present  an  opposite  condition  in 
these  respects.  Furthermore,  different  kinds  of  trees  and  plants  vary 
widely  in  their  adaptability  to  heavy  or  light  soils,  or  the  depth  of  soil 
which  they  require  for  proper  development.  Soils  which  are  entirely 
too  light  or  too  shallow  for  one  kind  of  tree  may  be  entirely  fitted  for 
another  kind.  Altogether,  therefore,  one  may  not  judge  too  hastily  or 
be  too  quick  either  to  condemn  or  approve  a  soil  for  a  certain  plant 
without  large  experience,  and  expert  knowledge  of  practical  conditions 
and  results  in  this  respect. 

The  methods  of  improvement  of  soils  of  poor  mechanical  structure 
form  a  subject  in  themselves  too  extensive  to  be  taken  up  in  this  place. 
Such  improvement  must  be  mainly  brought  about  in  one  of  two  ways : 
First,  through  cultural  operations,  such  as  deep  plowing  and  special 
cultivation;  second,  by  adding  materials  to  the  soil,  such  as  straw, 
manure,  or  green  manure  crops.  Special  treatises  on  this  subject  should 
be  consulted  for  information  along  these  lines. 

In  the  case  of  hardpan  of  limited  thickness  underlaid  by  good  soil, 
the  radical  practice  is  sometimes  resorted  to  of  blasting  with  powder  or 
dynamite,  blowing  out  a  hole  for  each  tree  before  it  is  planted.  Even 
in  established  groves,  blasting  between  the  trees  is  sometimes  done  with 
good  results.     ( See  Hilgard  's  ' '  Soils, ' '  page  181. ) 

Artificial  Influences  in  the  Soil. — Injury  to  plants  sometimes  occurs 
through  the  presence  in  the  soil  of  injurious  substances  which  have  come 
there  artificially  through  drainage,  or  by  being  placed  in  or  upon  the  soil. 
These  may  be  waste  substances  from  manufacturing  or  result  from  any 
one  of  a  great  variety  of  causes,  sometimes  wholly  unsuspected.  As  an 
instance  of  this,  we  may  cite  injury  to  citrus  trees  which  sometimes 
occurs  from  the  pouring  upon  the  ground  of  the  residue  of  sulphuric 
acid  and  potassium  cyanide  remaining  after  the  process  of  fumigation 
for  killing  scale  insects.  Sometimes  a  single  root  or  one  side  of  the 
trunk  will  be  affected  by  some  injurious  substance  of  this  sort,  and  the 
injury  reflect  itself  in  only  one  limb,  or  on  one  side  of  the  tree  corre- 


Bulletin  218]  CALIFORNIA  PLANT  DISEASES.  1075 

sponding  to  the  injured  portion  of  the  root  or  trunk.     Some  very  mys- 
terious cases  of  tree  disease  have  been  traced  to  this  source. 

A  not  infrequent  source  of  injury  to  trees,  particularly  street  trees, 
is  the  presence  in  the  soil  of  illuminating  gas  escaping  from  leaky  pipes. 
Great  damage  has  resulted  to  the  street  trees  of  many  cities  from  this 
source.  In  any  case,  where  street  trees  commence  to  fail  and  die  from 
no  apparent  reason,  this  sort  of  trouble  should  be  looked  for  if  there  is 
a  gas  pipe  in  the  street. 

INJURIES  BY  ANIMALS. 

Various  animals  are  injurious  to  cultivated  crops,  but  their  effects 
and  remedies  are  mostly  obvious,  and  need  no  special  consideration. 

The  most  serious  injury  of  this  sort  in  California  is  that  produced  by 
the  common  gopher,  which  is  one  of  our  greatest  pests.  These  animals 
feed  upon  the  roots  of  all  sorts  of  cultivated  plants  and  trees,  and  under 
favorable  conditions  become  very  numerous.  Their  most  evident  effects 
are  seen  where  plants  suddenly  wilt  and  die  on  account  of  the  roots  being 
eaten  off.  In  the  case  of  orchard  trees  of  considerable  size,  the  gopher 
often  works  on  the  bark  of  the  main  roots,  causing  the  tree  to  gradually 
decline  and  its  foliage  to  become  yellow,  finally  bringing  about  the  death 
of  the  tree.  It  may  linger  along  for  several  years,  however,  before  be- 
coming entirely  dead.  In  citrus  groves,  especially  where  gopher  control 
has  been  neglected,  trees  are  frequently  seen  with  foliage  of  a  bright 
yellow  color  and  covered  with  an  abnormally  large  number  of  small 
fruits.  Such  trees  are  an  almost  invariable  indication  of  gopher  attacks, 
and,  if  not  taken  in  hand  very  promptly,  will  soon  be  killed.  If,  how- 
ever, gophers  are  gotten  rid  of  before  the  injury  to  the  roots  has  gone 
too  far,  the  tree  may  form  new  bark  and  finally  recover.  In  such  cases, 
it  is  well  to  cut  the  top  back  to  an  extent  proportionate  to  the  amount 
of  injury  and  thus  give  the  tree  a  better  chance  to  recover. 

Gophers  can  only  be  kept  down  by  constant  warfare  through  the  use 
of  traps,  poison  and  shooting.  Special  traps  and  poisonous  preparations 
are  made  for  this  purpose,  some  of  which  are  very  effective.  See  bulletin 
172,  "The  Pocket  Gopher,"  Kansas  Experiment  Station,  Manhattan, 
Kansas. 

Squirrels,  moles,  and  other  similar  animals  often  cause  much  damage 
to  vegetation  and  are  to  be  controlled  by  means  of  the  nature  just 
alluded  to,  namely,  poisoning,  trapping,  and  shooting.  See  Circular 
76,  "The  California  Ground  Squirrel,' '  Bureau  of  Biological  Survey, 
United  States  Department  of  Agriculture.  See,  also,  Wickson  's  ' '  Cali- 
fornia Fruits,' '  page  410,  for  methods  of  control  of  gophers,  squirrels, 
rabbits,  etc. 

In  regard  to  rabbits,  we  quote  the  following  from  the  "California 
Cultivator' '  of  March  23,  1911 :  "According  to  the  experts  of  the  North 


1076  UNIVERSITY   OF    CALIFORNIA — EXPERIMENT    STATION. 

Dakota  Agricultural  College,  damage  to  trees  by  rabbits  gnawing  the 
bark  can  be  stopped  in  the  following  way:  Make  a  thick  whitewash; 
slaking  the  lime  over  night  improves  it.  To  each  pailful  of  the  white- 
wash add  three  tablespoonfuls  of  paris  green,  and  paint  the  trees  with  it. 
Stir  frequently  when  applying  it. ' ' 

Insects. — The  control  of  insect  pests  will  not  be  considered  in  this 
bulletin.  This  is  a  large  subject  in  itself  and  publications  are  available 
covering  most  of  our  common  pests. 

Worms. — One  organism  of  this  group  is  of  particular  importance  in 
connection  with  California  plant  diseases,  namely,  the  Nematode  Root 
Worm,  Heterodera  radicicola.  This  is  a  worm  of  microscopic  size,  which 
lives  parasitically  in  the  roots  of  many  different  plants,  causing  small 
nodules  or  galls  upon  them.  Such  nodules  are  quite  frequently  seen 
upon  the  roots  of  nursery  stock,  garden  vegetables,  and  other  plants, 
but  for  some  reason  this  organism  does  not  seem  to  become  serious  in 
this  State.  In  the  southeastern  portion  of  the  country  it  causes  serious 
damage  to  orchard  trees  and  other  plantings,  but  this  does  not  seem  to 
be  the  case  in  California. 

The  organism  in  question  is  hatched  from  eggs  which  are  deposited 
by  adult  female  worms  in  the  root  galls.  These  eggs  hatch  and  the 
young  worms,  which  are  so  small  as  to  be  quite  invisible  to  the  eye,  move 
about  in  the  soil  for  a  few  days  but  soon  burrow  into  the  tips  of  young 
roots  where  they  come  to  rest.  By  their  presence  in  the  roots  they  cause 
an  irritation  which  produces  a  swelling  and  the  formation  of  galls.  The 
mature  female  worms  can  be  seen  with  the  naked  eye  by  careful  exam- 
ination, being  little,  pearly-white,  pear-shaped  bodies,  about  the  size  of 
small  pin  head.  They  may  be  found  embedded  in  the  tissues  just 
beneath  the  surface  of  the  galls. 

This  form  of  injury  is  alluded  to  more  specifically  in  connection  with 
various  plants  in  a  later  portion  of  this  bulletin. 

Slugs  and  Snails. — These  creatures  are  frequently  the  cause  of  much 
damage  to  plants,  especially  in  moist  weather.  They  are  best  controlled 
by  sprinkling  dry  lime  dust  upon  the  ground  in  circles  about  the  plants, 
upon  the  leaves  of  the  plants  themselves,  or  in  any  way  so  that  the  slugs 
will  be  obliged  to  come  into  contact  with  the  lime.  This  is  very  repulsive 
to  them  on  account  of  its  irritating  effect  upon  their  soft  bodies.  They 
may  also  be  trapped  to  some  extent  by  laying  boards  upon  the  ground 
in  the  vicinity  of  the  plants  upon  which  they  feed,  thus  affording  a 
shelter  under  which  they  may  be  found  and  killed.  It  is  said  that  ducks 
are  particularly  fond  of  these  creatures. 

In  regard  to  snails,  we  find  the  following  in  the  Pacific  Rural  Press, 
of  June  12,  1909,  page  439 :    'These  pests  are  quite  common  in  England 


Bulletin  218]  CALIFORNIA  PLANT   DISEASES.  1077 

and  in  English  gardeners '  experience  a  mixture  of  salt  and  soot  scattered 
upon  the  ground  which  they  traverse  seems  to  be  most  effective.  Lime, 
which  is  something  of  a  protection  against  the  slug  branch  of  the  snail 
family,  does  not  seem  to  be  objectionable  to  the  shell  bearer." 

Fungi,  Bacteria,  and  Slime  Molds. — Organisms  of  this  sort  are  the 
cause  of  most  of  our  specific  plant  diseases,  and  these  are  described  in 
connection  with  their  particular  host  plants  in  the  following  alpha- 
betical list.  A  short  description  of  the  general  nature  of  these  organisms 
may  be  useful  at  this  point. 

Fungi. — The  organisms  called  fungi  are  true  plants  but  of  a  very 
low  order.  The  largest  and  most  highly  developed  members  of  the 
family  are  represented  by  the  toadstools,  mushrooms,  and  similar  plants. 
Other  common  examples  of  fungi  are  the  various  molds  and  mildews 
often  seen  growing  upon  different  organic  materials,  especially  in  moist 
air.  Only  certain  fungi  are  injurious  to  vegetation.  Those  species 
which  are  not  are  called  saprophytes.  These  grow  upon  dead  material, 
like  the  toadstools  which  we  see  upon  dead  wood  or  manure  and  the 
molds  which  develop  upon  decaying  fruit,  moist  leather,  bread  or  jelly. 
Many  kinds  of  fungi,  however,  are  able  to  grow  only  upon  the  tissues 
of  living  plants.  These  are  called  parasites.  Examples  of  this  are 
seen  in  the  rose  mildew,  a  mold-like  fungus  which  can  not  live  except 
upon  living  leaves,  and  the  various  rusts  which  have  the  same  habit. 
In  the  case  of  the  rust  most  of  the  fungous  plant  develops  in  the  interior 
tissue  of  the  leaf,  while  in  the  rose  mildew  it  grows  mostly  upon  the 
surface. 

It  is  characteristic  of  parasitic  fungi  that  in  most  cases  each  particular 
species  of  fungus  has  a  particular  species  of  plant  which  it  attacks,  or 
its  attacks  are  limited  to  a  few  closely  related  plants.  Certain  species 
of  rust,  for  instance,  attack  only  a  few  of  the  grains  or  grasses.  Another 
species  of  rust  attacks  the  asparagus,  but  the  asparagus  rust  fungus 
can  not  develop  upon  grain  nor  the  grain  rust  upon  the  asparagus  plant. 
Some  fungi  are  both  parasitic  and  saprophytic,  being  able  to  grow 
either  upon  living  plants  or  dead  matter.  Others  are  mainly  sapro- 
phytic but  may  become  parasites  upon  plants  in  a  weakened  or  un- 
healthy condition. 

The  body  of  a  fungous  plant  consists  usually  of  a  branching  mass  of 
very  fine,  thread-like  filaments  called  the  mycelium.  In  toadstools 
the  mycelial  filaments  become  very  abundant  and  mass  together  into 
structures  of  considerable  size  and  definite  form.  In  the  mold  fungi 
the  mycelium  develops  abundantly  under  favorable  conditions  and 
makes  a  cobweb-like  or  cottony  mass.  In  most  of  the  parasitic  fungi 
the  filaments  of  the  mycelium  grow  through  the  interior  tissues  of  the 
plant  attacked  (called  the  host  plant)  and  at  the  same  time  withdraw 


1078  UNIVERSITY   OF    CALIFORNIA — EXPERIMENT   STATION. 

nourishment  for  their  own  use.  They  also  sometimes  secrete  poisonous 
substances,  and  thus  are  caused  the  leaf  spots  or  dying  of  whole  leaves 
which  we  see  resulting  from  fungus  attacks.  Some  fungi  also  cause 
active  decay  of  fruit,  fleshy  roots,  tubers,  wood,  and  other  vegetable 
material.  The  reproductive  bodies  of  fungi,  corresponding  to  the  seeds 
of  higher  plants,  are  called  spores.  These  are  usually  very  small,  dust- 
like particles,  each  of  which  is  capable  of  sprouting  and  reproducing  the 
fungus  if  it  finds  favorable  conditions.  In  the  case  of  the  rusts  we  see 
the  spores  as  a  dusty  powder  which  develops  on  affected  plants.  Most  of 
the  common  molds  also  produce  a  dusty  mass  of  spores  on  the  surface 
of  the  mycelium. 

The  control  of  fungus  diseases  by  spraying  is  almost  always  effected 
by  covering  the  plants  with  the  poisonous  material  before  the  fungus 
has  made  its  attack,  thus  killing  the  spores  before  they  can  send  out 
sprouts  and  reach  the  interior  tissues.  If  the  latter  has  been  accom- 
plished and  the  fungus  is  already  inside  the  plant  nothing  can  then  be 
done  to  stop  its  effects  save  by  preventing  its  spread  to  other  leaves  or 
plants  not  yet  affected. 

Bacteria. — The  bacteria  are  organisms  of  even  simpler  nature  than 
the  fungi,  having  no  mycelial  body,  but  consisting  of  very  minute,  indi- 
vidual particles.  Each  of  these  individuals  is  able  to  multiply  very 
extensively  and  rapidly  by  division,  so  that  under  favorable  conditions 
bacteria  can  develop  in  sufficient  abundance  to  form  a  mass  visible  to 
the  eye.  Such  a  mass  of  bacteria  is  usually  of  a  slimy  nature,  as  seen 
in  fruit  and  vegetables  which  have  become  so  thoroughly  decayed  as  to  be 
in  a  semi-liquid  condition.  Most  of  the  bacteria  are  purely  saprophytes, 
living  only  on  dead  matter  and  producing  by  their  growth  decay,  fer- 
mentation, putrefaction  and  similar  processes.  A  number  of  species, 
however,  are  parasitic  on  animals,  causing  many  of  the  commonest  and 
most  serious  human  and  animal  diseases.  The  bacterial  plant  parasites 
are  fewer  in  number,  although  the  list  of  bacterial  plant  diseases  is 
gradually  growing.  Some  of  the  most  conspicuous  examples,  like  the 
pear  blight  and  walnut  blight,  develop  in  the  fresh,  succulent  tissues 
of  the  bark  or  in  the  fruit,  causing  the  death  of  the  parts  affected. 

It  should  be  said  in  connection  with  fungus  and  bacterial  diseases 
that  the  mere  finding  of  an  organism  of  this  sort  upon  a  diseased  plant 
or  any  of  its  parts  is  by  no  means  proof  that  the  organism  found  is  the 
cause  of  the  trouble.  If  a  leaf,  for  instance,  is  injured  in  any  way  so 
that  its  vitality  is  almost  or  quite  destroyed,  various  kinds  of  sapro- 
phytic fungi  or  bacteria  usually  develop  upon  it  very  quickly.  If  a 
plant  dies  or  becomes  very  much  weakened  from  any  cause  its  roots  soon 
begin  to  decay  and  various  saprophytic  soil  fungi  and  bacteria  will  be 
found  in  its  tissues.     It  is  practically  impossible  for  dead  or  dying  plant 


BULLETIN  218]  CALIFORNIA   PLANT   DISEASES.  1079 

tissue,  no  matter  how  it  was  first  affected,  to  remain  in  existence  without 
falling  prey  to  all  sorts  of  fungi  and  bacteria  which  would  have  no 
power  whatever  of  developing  upon  the  same  plant  when  in  a  healthy 
condition.  The  plant  pathologist  must,  therefore,  proceed  with  extreme 
caution  to  attribute  plant  troubles  to  organisms  of  this  sort  until  he  has 
absolutely  proven  that  the  initial  injury  was  produced  by  the  organism 
under  suspicion,  when  the  plant  was  still  in  a  healthy  condition.  To 
make  this  absolutely  certain,  he  must  not  only  find  the  organism  upon 
the  plant,  but  must  also  produce  all  the  characteristic  symptoms  of  the 
disease  by  inoculating  healthy  plants  of  the  same  species  with  his  fungus 
or  bacterium.  Long  experience  may  make  this  unnecessary  at  times 
and  obviate  much  tedious  work,  but  the  young  investigator  is  more  apt 
to  err  in  the  other  direction,  attributing  plant  troubles  to  fungi  or 
bacteria  which  really  had  nothing  to  do  with  them. 

Slime  Molds  (Myxomycetes) . — A  few  plant  diseases  are  caused  by 
organisms  of  this  class.  They  are  grouped  at  the  very  bottom  of  the 
vegetable  kingdom,  and  comprise  some  of  the  simplest  forms  of  life. 


A  LIST  Of  THE  MORE  SPECIFIC   PLANT   DISEASES   IN   CALIFORNIA, 
WITH  BRIEF  DIRECTIONS  FOR  TREATMENT. 

ALFALFA. 

Crown   Gall    (Urophlyctis  alfalfw).     Figure  7. 

Gall-like  swellings  appear  on  the  stems  and  main  roots  just  at  the 
surface  of  the  ground  and  the  plants  die.  The  trouble  is  favored  by 
excessive  moisture  in  the  soil.  Caused  by  a  fungus.  This  is  a  new 
disease  in  this  State,  and  has  not  been  reported  elsewhere  in  the  country 
at  this  writing. 

Allow  the  ground  in  affected  spots  to  dry  thoroughly  and  do  not  use 
it  again  for  some  time. 

Leaf  Spot  (Pseudopeziza  medicaginis) .     Figure  8. 

The  leaves  turn  yellow  and  die,  with  small,  dark  spots  upon  the 
surface.  The  trouble  is  not  a  serious  one  in  this  State,  and  needs  no 
special  treatment.     Caused  by  a  fungus. 

Cut  and  burn  the  crop  if  badly  affected. 

Rust  (Uromyces  striatus) . 
Reddish-brown,  dusty  pustules  break  out  in  small  spots  on  the  surface 
of  the  leaves.  This  trouble  is  caused  by  a  true  rust,  and  sometimes 
becomes  quite  destructive  to  alfalfa  during  the  rainy  season.  It  in- 
variably disappears  with  the  coming  of  dry  weather,  so  need  not  be 
seriously  feared. 

Cut  and  burn  badly  affected  crops. 


1080 


UNIVERSITY   OF    CALIFORNIA — EXPERIMENT    STATION. 


Fig.  7. — Crown  gall  of  alfalfa  (Urophlyctis  alfalfae), 


Bulletin  218] 


CALIFORNIA   PLANT   DISEASES. 


1081 


Stem  Rot  (Sclerotinia  libertiana). 
The  stems  wilt  and  die  after  reaching  nearly  full  size.  Usually  scat- 
tering stems  here  and  there  about  the  field  are  affected,  and  may  be 
easily  seen  by  their  contrast  with  the  thrifty,  green  appearance  of  the 
other  stalks.  This  trouble  usually  occurs  most  abundantly  where  there 
is  a  thick  stand  of  alfalfa,  heavily  shading  the  ground,  particularly  in 
the  spring  when  the  ground  is  very  moist.  On  pulling  an  affected  stem 
it  is  found  to  be  decayed  at  the  base,  and  usually  shows  a  more  or  less 
abundant  white  mold  upon  the  surface  if  there  is  an  abundance  of 
moisture.  In  this  mold  small,  roundish,  black  bodies  develop,  which 
represent  one  stage  of  the  fungus.  This  is  apparently  the  same  fungus 
which  causes  the  cottony  mold  decay  of  lemons   (page  1123)   and  also 


Fig.  8. — Leaf  spot  of  alfalfa    (Pseudopeziza 
medicaginis ) . 


stem  rot  of  various  other  plants.  It  causes  considerable  damage  to 
alfalfa  at  times  in  this  State,  and  it  has  been  reported  as  a  serious 
disease  in  other  States.  The  fungus  is  common,  affecting  various  plants 
all  over  the  world. 

No  specific  remedy  can  be  suggested,  but  the  disease  usually  disap- 
pears to  a  large  extent  during  the  summer  and  fall.  Badly  affected 
fields  should  be  plowed  up  and  used  for  some  other  crop  for  several 
years. 


1082 


UNIVERSITY   OP    CALIFORNIA — EXPERIMENT   STATION. 


Fig.  9. — Shot-hole  of  almond  (Cercospora  circumscissa) . 


Fig.  10. — Almond  rust    (Puccinia  pruni), 


Bulletin  218] 


CALIFORNIA    PLANT   DISEASES. 


1083 


Dodder  (Cuscuta). 

A  thread-like,  yellowish  vine  forms  a  thick  mat  in  the  alfalfa,  and 
becomes  parasitic  upon  it.  It  is  a  true  flowering  plant.  In  badly 
affected  fields  a  large  proportion  of  the  crop  is  lost  from  this  source. 
Allow  the  field  to  dry  out  for  some  time  and  the  dodder  will  often 


Fig.  11. — Crown  gall  of  almond  (Bacterium  tumefaciens) . 

be  entirely  killed  without  destroying  the  alfalfa  roots.     If  the  field  is 
badly  affected  plow  and  replant  later. 

Avoid  planting  infested  seed.  Dodder  seed  is  often  mixed  with  that 
of  alfalfa. 

ALMOND. 

Shot-hole   (Cercospora  circumscissa) .     Figure  9. 

There  appear  on  the  leaves  numerous,  small,  dead  spots,  which  finally 
fall  out,  giving  a  shot-hole  effect.  The  young  twigs  are  also  spotted. 
The  trees  are  sometimes  defoliated  early  in  the  season  by  this  fungus 
and  the  crop  badly  injured. 

Spray  with  Bordeaux  mixture  in  the  spring  as  the  buds  are  opening. 


1084  UNIVERSITY   OP    CALIFORNIA — EXPERIMENT   STATION. 

Rust   (Pnccinia  pruni).     Figure  10. 

Red  or  brown,  dusty  pustules  appear  on  the  under  side  of  the  leaves, 
usually  late  in  the  season.  The  fungus  may  hasten  the  normal  dropping 
of  the  leaves  somewhat  but  is  not  serious  on  thrifty  trees ;  worse  where 
the  trees  suffer  from  drouth. 

No  treatment  ordinarily  needed. 

Crown  Gall  (Bacterium  tumefaciens) .     Figure  11. 

Large  swellings  appear  on  the  main  root  just  below  ground  and  to 
some  extent  on  the  smaller  roots.  This  results  in  a  gradual  failure 
and  dying  of  the  trees.  This  is  one  of  the  commonest  troubles  of  our 
stone  fruit  trees,  being  found  both  in  the  nursery  and  on  mature  orchard 
trees.  This  trouble  is  caused  by  a  bacterial  organism  which  infests  the 
soil.  The  organism  would  seem  to  be  abundant  in  California  soils, 
since  cases  are  not  rare  of  infection  on  the  roots  of  trees  grown  from 
pits  in  virgin  soil. 

Avoid  planting  nursery  trees  in  affected  ground  and  in  orchard 
planting  discard  every  tree  which  shows  any  evidence  of  this  trouble. 
On  old  trees  the  galls  may  sometimes  be  chiseled  off  after  digging  down 
and  exposing  the  main  roots,  but  this  treatment  is  not  usually  very 
satisfactory.  Disinfect  the  cuts  with  strong  bluestone  or  corrosive 
sublimate  solution. 

Root  Rot — Oak  Fungus.     Figure  12. 

Many  orchards  of  almonds  and  other  trees  contain  certain  spots 
where  the  trees  commence  dying  from  a  center,  the  trouble  gradually 
proceeding  outward  in  a  circle,  involving  tree  after  tree.  Clusters  of 
toadstools  frequently  appear  about  the  base  of  affected  trees  in  the 
winter.  These  spots  usually  coincide  with  places  where  oak  trees 
formerly  stood  and  the  destruction  of  the  fruit  trees  is  due  to  certain 
' '  toadstool ' '  fungi  which  apparently  live  on  the  old  oak  roots  and  spread 
through  the  soil,  infecting  the  roots  of  the  orchard  trees.  Several  dif- 
ferent fungi  seem  to  cause  this  disease,  among  which  Armillaria  mellea 
is  probably  the  most  important. 

The  progress  of  the  trouble  may  be  checked  by  digging  a  deep  trench 
around  the  affected  area,  but  this  is  impracticable  in  most  cases. 

The  development  of  a  resistant  root  presents  the  only  practical 
remedy. 

The  pear  root,  fig  and  that  of  the  California  black  walnut  are  some 
of  the  most  resistant  among  fruit-bearing  trees  and  these  may  usually 
be  planted  with  safety.  The  cherry  is  the  most  resistant  of  the  stone 
fruits. 

Fruit  Drop. 

The  fruit  falls  to  the  ground  while  still  very  small  and  undeveloped. 
Due  partly  to  seasonal  conditions  which  can  not  be  controlled,  and 
partly  to  a  lack  of  cross  pollination,  which  can  be  secured  by  mixing 


Bulletin  218] 


CALIFORNIA    PLANT   DISEASES. 


1085 


varieties  in  planting.  Heavy  rains  at  the  time  of  blossoming  may  have 
this  effect,  and  it  may  also  be  produced  by  frost,  killing  the  young  germ 
in  the  seed  of  the  fruit.  Many  other  fruits  are  affected  in  the  same 
way,  such  as  the  apricot,  cherry,  peach,  and  pear.  The  fruit  may 
remain  on  the  tree  and  continue  to  grow  in  size  for  some  time  before 
dropping. 


Fig.  12. — Root  rot  caused  by  the  toad-stool  fungus   (Armillaria 

mellea)  on  live  oak. 

Sour  Sap. 
"When  affected  with  this  trouble  the  tree  may  suddenly  die  just  as  it 
is  coming  out  in  the  spring  in  full  vigor,  or  the  effect  may  be  limited 
to  one  limb  or  one  portion  of  the  tree,  which  dies  after  the  leaves  have 
started,  or  even  after  the  fruit  is  partly  grown.  All  our  stone  fruits 
suffer  frequently  with  the  disease  characterized  by  this  name,  while 
4— Bul.  218 


1086 


UNIVERSITY   OF    CALIFORNIA — EXPERIMENT    STATION. 


occasionally  the  pear  and  other  trees  are  affected.  The  trouble  appears 
to  be  due  entirely  to  climatic  conditions  resulting  from  a  combination 
of  unseasonably  warm,  balmy  weather  in  winter,  followed  by  a  marked 
change  to  colder  weather.  The  sap  of  these  trees  frequently  starts  into 
active  circulation  with  the  first  approach  of  spring,  and  when  this 
occurs  too  early  in  the  season,  cold  weather  following  suddenly,  checks 
the  flow  of  sap  and  other  functional  activities  of  the  tree,  causing  a 
stagnation  and  finally  fermentation. 

Affected  trees  should  be  pruned  back  to  healthy  wood,  where  there  is 
enough  remaining  to  make  a  new  top. 


Fig.  13. — Die-back  of  orchard  trees. 

Die-Back. 
Numerous  more  or  less  abandoned  groves  of  almonds,  as  well  as  other 
deciduous  fruit  trees,  are  to  be  seen  in  California  which  present  a  dis- 
tressing appearance  on  account  of  a  dying  back  of  the  branches.  In 
some  cases  the  trees  are  entirely  dead,  while  in  others  they  show  all 
stages  of  deterioration.  The  trouble  in  the  majority  of  these  cases  is 
due  primarily  to  a  lack  of  water  induced  by  a  variety  of  causes,  either 
an  absolute  lack  of  sufficient  moisture  during  the  year  to  keep  the  trees 
alive,  or  unfavorable  soil  conditions,  such  as  hardpan,  gravel,  and  similar 


Bulletin  218] 


CALIFORNIA    PLANT   DISEASES. 


1087 


troubles.  Lack  of  soil  fertility  is  frequently  a  contributory  factor. 
Such  cases  of  die-back  are  connected  usually  with  some  of  the  unfavor- 
able soil  conditions  which  we  have  described  in  connection  with  that 


Fig.  14. — Apple  twig  affected  by  mildew   (Podosphaera  oxyacanthae) . 

subject.  In  the  majority  of  cases  these  plantings  were  doomed  to  failure 
from  the  start  and  represent  an  ill-advised  undertaking,  or  in  some  cases 
criminal  deception.     Various  secondary  causes  may  contribute  to  the 


1088 


UNIVERSITY   OF    CALIFORNIA — EXPERIMENT   STATION. 


dying  of  such  trees  as  we  have  described,  but  such  factors  are  usually 
of  little  importance,  and  in  many  cases  are  an  actual  blessing  to  the 
owner  in  hastening  the  time  when  his  expenditures  for  the  maintenance 
of  such  an  orchard  are  brought  to  an  end. 


APPLE. 

Mildew    (Podosphacra  oxyacanthw) .     Figure  14. 
Characterized  by  a  dwarfing  of  the  tips  of  the  new  shoots,  which, 
together  with  the  leaves  which  they  bear,  remain  stunted  and  covered 


^WHfh, ,1 


Fig.  15. — Apple  scab  (Venturia  inaequalis) . 

with  the  white  mildew  growth  of  the  fungus.  Much  worse  on  some 
varieties  than  others. 

Has  not  been  controlled  very  successfully  heretofore,  but  good  results 
have  been  obtained  in  some  instances  by  spraying  quite  frequently 
through  the  early  part  of  the  season,  commencing  just  before  the  buds 
unfold,  with  sulphide  sprays.     (See  page  1187.) 

Some  growers  report  success  from  spraying  with  the  caustic  soda- 
sulphur  spray,  about  10  pounds  of  dry  sulphur  being  added  to  each  50 
gallons  of  spray. 


Bulletin  218]  CALIFORNIA  PLANT  DISEASES.  1089 

The  iron  sulphide  spray  mentioned  on  page  1187  is  said  to  be  partic- 
ularly effective  for  mildew  in  the  Pajaro  Valley. 

Scab   (Venturia  inaequalis) .     Figure  15. 

Easily  identified  by  the  scabby  patches  produced  on  the  surface  of  the 
fruit,  in  which  the  brown,  velvety  growth  of  the  fungus  can  be  seen. 

Spray  with  Bordeaux  mixture  just  as  the  buds  are  opening,  again 
after  the  petals  fall,  and  once  or  twice  at  intervals  later,  where  the 
variety  or  location  is  particularly  susceptible.  Arsenate  of  lead  or 
paris  green  for  codling  moth  may  be  combined  with  this  spray. 

Blight    (Bacillus  amylovorus) . 

See  pear  blight,  which  is  caused  by  the  same  organism.  Blight  is  not 
usually  as  destructive  in  apples  as  in  pears,  except  occasionally  with 
very  susceptible  varieties.  Its  worst  effect  in  apples  usually  consists  in 
killing  the  blossoms  and  thus  destroying  the  crop,  rather  than  causing 
the  death  of  large  limbs  or  whole  trees.  Sometimes  the  disease  runs 
down  into  the  large  limbs  and  may  remain  alive  there  from  year  to  year, 
forming  a  source  of  infection  to  neighboring  pear  and  apple  orchards. 
More  often  the  infection  proceeds  only  to  the  base  of  the  fruit  spurs, 
killing  the  twigs  to  that  point. 

Destroy  old,  worthless  apple  trees  standing  in  the  vicinity  of  valuable 
apple  or  pear  orchards. 

Root  Hot. 
The   " toad-stool' '   disease,   described  for   the   almond,    occasionally 
affects  young  apple  trees  recently  set  out,  but  it  is  not  usually  serious 
on  established  trees. 

Stem  Rot   (Schizophyllum  commune) .     Figure  16. 

.  This  is  another  toad-stool  disease,  affecting  the  tree  above  ground. 
The  fungus  in  question  shows  itself  in  clusters  of  small,  bracket-like 
growths  which  appear  on  dead  portions  of  the  trunk  or  branches.  This 
fungus  infects  the  tree  through  wounds  caused  by  pruning  or  any 
injury  and  in  some  cases  develops  rapidly  in  the  heart  wood  of  young 
trees,  extending  far  up  in  the  trunk  and  out  into  the  branches,  while 
the  bark  is  still  green  and  healthy  and  the  whole  tree  appears  to  be  in 
good  condition.  From  the  heart  wood  the  fungus  gradually  works  out 
into  the  outer  sap  wood  and  cambium,  killing  the  tree.  Affected  trees 
often  appear  in  good  condition  at  the  end  of  the  growing  season  in  the 
fall,  but  are  found  to  be  dead  the  following  spring  when  they  fail  to 
leaf  out.  This  sudden  effect  is  produced  by  the  development  of  the 
fungus  into  the  sap  wood  and  cambium  during  the  winter  while  the 
tree  is  dormant  and  more  susceptible. 

Make  all  pruning  cuts  cleanly  and  close  to  the  trunk,  and  paint  over 


1090  UNIVERSITY  OF   CALIFORNIA — EXPERIMENT   STATION. 


Fig.  16. — Canker  of  apple  limbs  caused  by  the  fungus  Schizophyllum. 


Bulletin  218] 


CALIFORNIA   PLANT   DISEASES. 


1091 


the  scars  with  thick  lead  paint.     In  cases  of  trees  unavoidably  injured 
the  wounds  should  be  treated  in  the  same  manner  as  soon  as  possible. 

Sun  Burn.     Figure  17. 

The  bark  on  one  side  of  the 
trunk  dies  and  the  wounds  thus 
produced  frequently  become  in- 
fected with  the  little  Schizo- 
phyllum  fungus  just  described. 
The  apple  is  quite  susceptible 
to  winter  sun  burn  injury  of  the 
trunk  and  large  branches.  Es- 
pecially in  the  higher  foothill 
regions,  where  in  late  winter 
and  spring  the  days  are  hot 
and  the  nights  cold,  trouble  of 
this  sort  often  occurs,  as  de- 
scribed on  page  1054. 

Paint  the  trunks  with  thick 
whitewash,  and  keep  the 
ground  about  the  trees  covered 
in  winter  with  vegetation  or  a 
mulch  of  some  sort. 


Fig.  17. — Effect  of  sun  burn  on  trunk  of  apple 

tree. 


Fig.  18. — Fruit  spot  of  apple. 


1092 


UNIVERSITY   OF    CALIFORNIA — EXPERIMENT   STATION. 


Die-Back.     See  Almond. 
Fruit  Spot.     Figure  18. 

Characterized  by  the  appearance  of  sunken,  discolored  spots  on  the 
surface  of  the  apple,  beneath  which  the  tissue  is  found  to  be  brown  and 
dead.  The  dead  tissue  also  extends  to  a  considerable  extent  in  streaks 
and  lines  through  the  flesh  of  the  apple.  This  effect  may  show  while 
the  apple  is  still  on  the  tree  or  sometimes  develops  only  after  the  fruit 
has  been  picked  for  some  time.  The  trouble  has  been  ascribed  to  various 
causes.  This  disease  is  similar  to  that  called  "brown  spot"  or  "Bald- 
win spot"  in  other  portions  of  the  country. 

No  cause  or  remedy  satisfactorily  demonstrated  in  California. 


Fig.  19. — Storage  spot  of  apple. 
Storage  Spot. 

Numerous  dark,  dead  spots  appear  on  apples  after  being  in  storage 
for  some  time,  usually  on  the  upper  side  of  each  apple  as  it  lies  in  the 
box.  Especially  common  on  the  White  Winter  Pearmain,  but  also  found 
on  Jonathan  and  other  varieties. 

Cause  not  definitely  known,  but  in  storage  not  due  to  freezing.  Has 
recently  been  attributed  to  after-effects  of  arsenical  insecticides. 


Bulletin  218] 


CALIFORNIA    PLANT   DISEASES. 


1093 


Hollow  Apple.  Figure  20. 
A  peculiar  condition  found  in  one  or  two  instances..  The  affected 
fruit  is  sunken  in  on  one  side  and  has  a  misshapen  appearance.  On 
cutting  through  the  apple  large  hollow  cavities  are  found  corresponding 
to  the  sunken  areas  on  the  surface.  Due  apparently  to  some  injury- 
while  the  fruit  was  small. 


Fig.  20. — Hollow  apple. 

Club  Tip. 

Terminal  buds  die  back  or  fail  to  grow  and  enlarged  swellings  develop 
at  the  ends  of  the  living  portion  of  the  twigs.  Lateral  shoots  may 
develop  later  from  these.     Affects  some  varieties  more  than  others. 

Due  apparently  to  unfavorable  soil  or  climatic  conditions  which  check 
the  growth  of  the  terminal  buds.  Sometimes  caused  by  apple  mildew. 
No  remedy,  save  in  latter  case,  which  see. 

Seasonal  Effects.  Figure  21. 
Apple  trees  in  California,  particularly  in  the  valleys,  are  sometimes 
affected  by  the  seasonal  diseases  described  on  page  1151.  These  effects 
show  themselves  in  die-back,  blooming  out  of  season,  failure  of  the  buds 
to  open  at  the  proper  time,  " Little  Leaf,"  and  a  stunted,  weak  growth 
of  the  shoots.  Such  effects  are  produced  most  commonly,  perhaps,  by  a 
long,  dry  season  in  the  fall,  causing  the  trees  to  become  especially  dor- 


1094 


UNIVERSITY   OF    CALIFORNIA — EXPERIMENT   STATION. 


mant,  followed  by  warm,  spring-like  weather  during  the  winter  soon 
after  the  first  rains.  Again,  they  may  be  produced  by  long,  continuous 
rainfall  during  the  winter,  followed  by  a  very  sudden  end  of  the  rainy 
season  and  a  long  period  during  the  spring  and  early  summer  of  hot, 
dry  weather.  These,  and  other  irregular  combinations  may  produce 
the  effects  described  and  other  similar  ones. 


Fig.  21. — Little  leaf  of  apple. 


Bulletin  218] 


CALIFORNIA   PLANT   DISEASES. 


1095 


APRICOT. 
Shot-Hole  and  Fruit  Spot    (Coryneum   beyerinkii).     Figure  22. 
This  fungus  is  the  same  as  that  causing  the  peach  blight  and  produces 
in  the  apricot  a  spotting  of  the  fruit,  shot-hole  effect  in  the  leaves  and 
killing  of  the  buds. 

Spray  with  Bordeaux  mixture  during  November  and  again  in  spring 
just  as  the  buds  open. 

See  bulletin  203,  page  33,  California  Experiment  Station. 


Fio.  22. — Apricot  shot-hole  and  leaf  spot    (.Coryneum   beyerinkii), 


1096 


UNIVERSITY   OF    CALIFORNIA — EXPERIMENT   STATION. 


Fig.  23. — Apricot  bud  blight. 
Bud  Blight.     Figure  23. 
Characterized  by  a  dying  of  the  buds  during  the  early  winter  and 
caused  very  largely  by  the  fungus  just  mentioned. 

Similar  trouble  is  caused  more  or  less  by  "Sour  Sap"  conditions. 


Bulletin  218]  CALIFORNIA  PLANT  DISEASES.  1097 

Scab    (Cladosporium   carpophilum) .     Figure   24. 
Causes  a  scabby  spotting  on  the  surface  of  the  fruit. 
Has  never  been  sufficiently  serious  to  warrant  treatment  in  California. 

Brown  Rot  (Sclerotinia  fructigena).  Figure  20. 
A  decay  of  the  fruit  while  still  on  the  tree,  occurring  some  seasons  in 
the  vicinity  of  San  Francisco  Bay  and  other  moist  localities.  The  young 
growth  as  well  as  the  fruit  is  also  sometimes  affected,  the  new  shoots 
wilting  and  dying  back  from  the  attacks  of  this  fungus.  This  is  the 
most  serious  obstacle  to  stone  fruit  production  in  the  eastern  states,  but 
does  not  find  sufficient  moisture  for  its   development   in   California, 


Fig.  24. — Apricot  scab  (Cladosporium  carpophilum) . 

except  on  early  varieties  in  occasional  seasons  of  late  rains  in  the  local- 
ities mentioned  above. 

No  definite  remedy  for  this  trouble  has  been  demonstrated  in  Cali- 
fornia, but  spraying  with  self-boiled  lime  sulphur  just  as  the  fruit  is 
setting  and  again  with  the  same  following  subsequent  rains  is  recom- 
mended for  trial. 

See  bulletin  203,  page  39,  California  Experiment  Station. 

Blossom  Rot.     Figure  26. 

The  young  fruit  decays  while  still  very  small  and  enclosed  by  the 
calyx  or  outer  cup  of  the  blossom.  The  trouble  occurs  when  wet  rainy 
weather  prevails  during  the  time  of  fruit  setting.  It  commences  in  a 
rotting  of  the  calyx  cup,  which  is  dead  and  susceptible  to  decay  by 
saprophytic  fungi,  which  decay  spreads  to  the  young  fruit.  It  is  caused 
by  various  fungi,  of  which  perhaps  a  species  of  Sclerotinia,  apparently 
8.  libertiana,  is  most  common,  causing  a  decay  of  the  young  fruit  on  the 
tree.  When  such  fruit  is  picked  and  placed  in  moist  chamber  it  develops 
an  abundant  cottony  mold  in  which  black  sclerotia  soon  forms.  This 
appears  to  be  the  same  fungus  causing  the  cottony  mold  or  white  rot  of 


1098 


UNIVERSITY   OF    CALIFORNIA — EXPERIMENT   STATION. 


the  lemon  storage.     Botrytis  vulgaris  is  also  common  in  this  trouble. 
Same  treatment  as  brown  rot. 


Fig.   25. — Brown  rot  of  apricot   (Sclerotinia  fructigena) . 

Spraying  for  shot-hole  fungus  might  also  be  of  some  benefit  in  this 
trouble. 

Fkuit  Drop.     See  Almond. 

Sour  Sap  and  Seasonal  Effects. 

The  apricot  is  particularly  sensitive  to  sour  sap  (see  Almond)  and 
other  seasonal  effects.  It  is  a  tree  having  a  free  flow  of  sap,  quick  to 
respond  to  stimulating  influences  and  one  having  the  characteristic  of 
all  the  stone  fruits  of  forming  an  abundance  of  gum  when  injured  in 
any  manner.     On  this  account,  if  any  active  sap  movement  from  the 


Bulletin  218] 


CALIFORNIA   PLANT   DISEASES. 


1099 


Fig.  26. — Apricot  calyx  rot    (Sclerotinia  Hbertiana). 

roots  is  started  early  in  the  season  by  warm  weather  or  an  abundance  of 
moisture  and  this  activity  be  checked  again  by  less  stimulating  weather 
conditions,  trouble  is  very  apt  to  follow.  The  sap  becomes  stagnant  in 
the  tissues,  full  of  sugars  and  other  easily  fermentable  substances,  gum 
begins  to  form,  sun  burn  may  also  occur  and  very  often  severe  injury 
take  place  in  the  tissues  of  the  sap  wood  and  cambium  layer. 


1100 


UNIVERSITY   OF    CALIFORNIA — EXPERIMENT   STATION. 


Crown  Gall  and  Root  Rot.     See  Almond. 
Die-Back.     See  Almond. 
Gummosis.     See   Cherry. 

ASPARAGUS. 
Rust   (Puccinia  asparagi).     Figures  27  and  28. 

Causes  premature  death  of  the  bushy  tops 
which  grow  up  after  the  cutting  season,  thus 
injuring  the  vitality  of  the  plants.  The 
fungus  causing  the  rust  shows  three  different 
stages,  the  spring  rust,  appearing  in  the 
form  of  elliptical  patches  on  the  stems  of 
plants  which  are  allowed  to  grow  up  early 
in  the  season,  the  summer  or  red  rust,  which 
covers  the  tops  with  a  reddish,  dusty  powder 
of  spores  during  the  summer,  causing  their 
death,  and  the  black  rust  stage,  which  ap- 
pears on  the  tops  in  the  form  of  numerous 
black  pustules  following  the  red  rust. 

During  the  cutting  season  allow  no  wild 
asparagus  to  grow  up. 

Keep  the  fields  well  irrigated  and  culti- 
vated during  the  summer  and  fall  after  cut- 
ting stops.  Dust  the  tops  thoroughly  with 
flowers  of  sulphur  about  three  weeks  after 


Fig.    27.  —  Asparagus  rust, 
winter   stage. 


Fig.  28. — Asparagus  rust,  summer  stage. 


Bulletin  218] 


CALIFORNIA   PLANT   DISEASES. 


1101 


the  cutting  season  ends  and  repeat  this  two  or  three  times  during  the 
remainder  of  the  season.    . 

Select  seed  for  planting  from  the  most  rust-resistant  plants.     See 
Bulletins  165  and  172,  California  Experiment  Station. 

ASTER. 

Yellows. 

Characterized  by  the  production  of  sickly,  yellow  shoots  and  abortion 

of  the  flowers.     Apparently  caused  by  climatic  conditions.     Not  very 

serious  in  California.     No  remedy  known. 

BARLEY. 

Closed  Smut  (Ustilago  hordei). 

The  grain  is  turned  a  dark  color  by 
the  formation  of  the  fungus  spores  in  its 
substance.  This  remains  firm  rather 
than  flying  out  in  a  dusty  mass,  as  in  the 
next  form. 

Loose  Smut  (Ustilago  nuda).     Figure  29. 

Differs  from  the  last  in  that  the  smutty 
substance  of  the  grain  scatters  out  in  the 
form  of  black  dust,  leaving  the  heads 
empty. 

Barley  is  not  often  affected  with  smut 
in  California,  so  that  we  can  not  distin- 
guish as  to  the  occurrence  of  these  two 
different  species.  It  is  advisable,  how- 
ever, to  treat  the  seed  as  follows : 

Soak  for  10  minutes  in  one  of  the  fol- 
lowing solutions : 

1.  Bluestone 1  pound  to  5  gallons  of  water. 

2.  Formalin 1  pint  to  30  gallons  of  water. 

The  seed  should  be  soaked  long  enough 
to  get  every  grain  thoroughly  wet  and 
then  immediately  taken  out.  If  not 
planted  at  once  the  grain  must  be  dried 
before  storing.  Plant  a  little  more  seed 
after  this  treatment  than  would  be  used 
with  untreated  grain. 

Loose  smut  alone  is  more  successfully 
controlled  by  the  following  seed  treat- 
ment : 
in  cold  water  for  5  hours.     Then  soak  in  water  at  a  temperature 
degrees  F.  for  15  minutes.     The  proper  temperature  must  be 


Fig.  29. — Loose  smut  of  barley 
(Ustilago  nuda). 


Soak 
of  125 

5_Bul.  218 


1102 


UNIVERSITY   OF    CALIFORNIA EXPERIMENT    STATION. 


carefully  maintained  to  make  this  treatment  successful,  but  it  is  not 
usually  necessary  in  California. 

Blade    Blight    (Helminthosporium    gramineum) .     Figure    30. 

The  leaves  turn  yellow  and  are  covered  with  elongated  black  spots. 
This  is  frequently  seen  in  unfavorable  seasons  when  the  plants  are  small 
and  rather  stunted.  The  plants  usually  overcome  the  diseased  condi- 
tion when  weather  conditions  are  favorable. 

It  is  a  question  whether  the  primary  trouble  is  not  caused  by  weather 
conditions  more  than  by  the  fungus.  In  periods  of  long 
continued,  cold  rain  in  winter,  to  which  barley  is  often 
subjected,  the  plants  grow  very  feebly,  turn  yellow  and 
form  their  roots  close  to  the  surface  of  the  water-soaked 
ground.  "When,  as  sometimes  happens,  the 
seasonal  rain  suddenly  ends  and  hot,  dry 
windy  weather  follows,  the  surface  soil 
dries  out  suddenly,  the  shallow-rooted  bar- 
ley is  left  without  moisture  and  the  al- 
ready weakened  plants  fall  an  easy  prey 
to  fungi. 

No  remedy  feasible  or  commonly  needed. 


BEAN. 

Mildew  (Erj/siphe  polygoni). 

Produces  a  white  growth  of  the  fungus 
covering  the  surface  of  the  leaves  in  moist 
weather. 

Sprinkle  with  dry  sulphur. 

Rust  (TJromyces  appcndiculatus) . 

Causes    a   yellowing   and   death   of   the 

leaves  with  the  production  of  a  dusty  red 
rust  on  the  under  side.  Not  usually  de- 
structive except  on  plants  growing  poorly. 


,,/ 


Spot  {Collet otrichum  lindemuthianum) .     Figure  31. 

Causes  large,   scabby,   dead  spots  upon 

the  pods.     Not  often  serious  in  this  State. 

May  be  controlled  by  selecting  clean  seed 


Fig.    31. — An- 
thracnose     of" 


Fig.  30. — Blade 
blight  of  bar- 
ley   (Heimin-  and   spraying   the   plants   with   Bordeaux  bean     (Coiieto- 

thospor  ium        .  trichum      linde- 

grarmneum).     mixture.  muthianum). 

BEET. 
Rust  (Uromyces  oetm) . 

A  typical  red  rust  on  the  leaves,  common  on  sugar  and  garden  beets, 
if  grown  during  the  rainy  season.     Not  serious. 


Bulletin  21S] 


CALIFORNIA   PLANT    DISEASES. 


1103 


Fig.  32. — Leaf  spot  on  beet   {Cercospora  beticola). 

Leaf  Spot  (Cercospora  beticola).     Figure  32. 
Produces  small  dead  spots  all  over  the  leaves.     Quite  common  in 
California,  but  practically  unknown  on  sugar  beets. 

Downy  Mildew   {Peronospora  schachtii).     Figure  33. 
Causes  a  stunting  of  the  inner  leaves  and  a  checking  of  the  growth 
of  the  plant.     The  fungus  is  visible  to  the  eye  as  a  mildew  on  the  under 


1104 


UNIVERSITY   OF    CALIFORNIA — EXPERIMENT    STATION. 


side  of  the  affected  leaves  in  the  center  of  the  plant.     Found  recently 
in  California  on  sugar  beets,  this  being  the  first  report  in  this  country. 
Not  yet  serious.     Occurs  only  during  the  rainy  season. 
When  found,  the  plants  should  be  pulled  and  destroyed. 

Root  Rot  (Rhizoctonia) . 
Appears  in  young  plants  as  a  decay  of  the  main  root.     Does  not 
usually  kill  the  plant  but  causes  the  root  to  fork  and  become  misshapen. 
Not  very  serious. 

Curly  Top — Blight.     Figures  34  and  35. 
Characterized  by  thickened,  curled  leaves,  stunted  growth,  an  abun- 
dance of  fibrous  roots  and  a  pronounced  blackening  of  the  concentric 


Fig.   33. — Downy  mildew  of  beet   (Peronospora  schachtii). 

rings  in  the  interior  of  the  beet.  Our  most  serious  sugar  beet  disease. 
The  cause  of  this  disease  has  recently  been  found  to  be  an  insect 
( Eutettix) ,  but  its  development  is  very  largely  influenced  by  climatic 
conditions. 

Avoided  largely  by  determining  the  best  time  for  planting  in  affected 
localities. 

See  bulletin  184,  page  240,  California  Experiment  Station. 

Root  Knot   (Nematode). 
Produces  small;  gall-like  swellings  on  the  roots.     Has  been  found  in 
California  but  does  not  seem  to  have  become  serious.    See  page  1076. 


Bulletin  218] 


CALIFORNIA   PLANT   DISEASES. 


1105 


Fig.   34. — Curly  top  of  beet. 


1106 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION. 


Fig.  35. — Curly  top  of  beet.     Sections  showing  blackened  fibrovascular  rings. 


Bulletin  21 S J 


CALIFORNIA    PLANT    DISEASES. 


1107 


Produces  bright 
orange  masses  of 
spores  all  over  the 
under  side  of  the 
Leaves.  The  fungus 
spreads  all  through 
the  plant  so  that  it 
is  not  easily  con- 
trolled. 

Cut  affected 
plants  to  the 
ground  and  burn. 
Spray  new  growth 
with  Bordeaux 
mixture. 


BLACKBERRY. 

Rust  (Oymnocotiia  int ers tit alls ) . 


Fig- 


Leaf  Spot 
(Septoria  rubi). 
ure  36. 

Produces  small 
dead  spots  on  the 
leaves.  Not  usu- 
ally very  serious. 

Spray  with  Bor- 


Fig.   37. — Fruit   rot  of  blackberry 
(Botrytis  vulgaris). 


Fig.  36. — Leaf  spot  of  blackberry   {Septoria  rubi). 

deaux  mixture  about  four 
times  at  short  intervals  (of 
about  ten  days),  the  first 
application  when  the  buds 
are  beginning  to  unfold. 

Crown  Gall 
( Bacterium    tumefaciens ) . 

Produces  large  swellings 

or  galls  just  below  ground. 

Destroy  affected  plants  and 

use  care  in  planting  clean 

stock. 

Fruit  Rot  (Botrytis).     Fig- 
ure 37. 

The  ripe  fruit  decays  on 
the  bushes  and  is  covered 
with  a  grey,  dusty  mold. 
Usually  not  abundant  ex- 
cept in  moist  weather. 

No  treatment  feasible. 
All  affected  fruit  should  be 


1108 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION. 


discarded  and  not  mixed  with  that  which  is  unaffected,  as  the  rot  will 

spread  after  picking. 

CABBAGE. 

Club  Foot    (Plasmodiophora  brassiccc). 

Produces  large  swellings  on  the  roots  and  stunting  or  death  of  the 

plants.     Not  common  in  California. 

Black  Rot    (Pscndomonas  campestris). 

This  bacterial  disease  causes  the 
ruin  of  the  heads,  the  veins  of  the 
leaves  turning  black  and  decay- 
ing. The  trouble  is  very  uncom- 
mon in  California  if  it  occurs  at  all. 

CARNATION. 

Rust  (Uromyces  caryophyllinus) . 

Produces  pustules  containing  the 
reddish,  dusty  spore  masses  of  the 
fungus  on  the  leaves.  Not  serious 
on  healthy  plants  in  this  State. 

Wilt — Stem  Rot   (Fusarium). 
Causes  a  dry  rot  of  the  stem  and 
root    tissue    of    the    plant.       Not 
serious. 

Leaf   Spot    (Heterosporium   echinulatum 
and  Septoria  dianthi).     Figure  38. 

Produces  dead  spots  on  the 
leaves.  Not  important  in  this 
State. 

This  disease,  together  with  the 
rust,  may  be  controlled  to  some  ex- 
tent by  spraying  with  Bordeaux 
mixture  if  necessary.  In  both  cases 
use  care  in  selecting  healthy  cut- 
tings for  propagation  and  grow 
them  in  fresh  soil. 


Fig.      38. — Leaf     spot     of     carnation 
( Heterosporium   echinulatum ) . 


CELERY. 

Summer  Blight   (Cercospora  apii). 
Produces  large,  irregular  dead  spots  on  the  leaves  during  the  summer. 
Quite  common  in  moist  localities  but  not  serious. 

Winter  Blight    (Septoria  petroselini,   var.    apii).     Figure   39. 
Produces  smaller  spots  than  the  last,  with  numerous  black  pustules 
dotting  them.     Develops  more  during  the  rainy  season,  especially  if  the 
growth  of  the  plants  is  checked  by  unfavorable  conditions.     The  disease 


Bulletin  218] 


CALIFORNIA    PLANT    DISEASES. 


1109 


affects  mostly  the  older  outside  leaves,  causing  a  stunting  of  the  plant 
and  also  decay  in  shipment. 

Spray  frequently  with  Bordeaux  mixture  at  all  times  during  the 


Fig.   39. — Winter  blight   of  celery    (Septoria  petroselini). 

growth  of  the  plant,  from  the  seed  bed  up  to  maturity,  whenever  there 
is  much  moisture  in  the  air. 

See  Bulletin  208,  California  Experiment  Station. 

Stem  Rot  (Sclerotinia). 
Causes  a  reddish,  soft  decay  of  the  stalks. 

Root  Rot   (Fusarium). 

A  decay  of  the  roots.     Both  this  and  the  last  occur  only  when  the  land 

is  wet  and  heavy  and  the  plants  growing  poorly.     Neither  is  common 

nor  serious. 

CHERRY. 

Brown  Rot   (Sclerotinia  fructigena) .     See  Apricot. 

Root  Rot.     See  Almond. 

Gummosis. 

The  cherry,  like  other  stone  fruit  trees,  is  very  subject  to  gumming 

of  the  trunk  and  branches,  as  a  result  of  any  injury.     In  seasons  of 

heavy  rains  during  the  spring  cherry  trees  frequently  show  a  trouble 


1110 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION. 


of  this  sort  quite  similar  to  that  of  citrus  trees.  Masses  of  gum  break 
out  on  the  trunk  and  the  trees  frequently  die.  Young  trees  are  some- 
times affected  much  like  citrus  trees,  the  gum  breaking  out  just  at 
the  surface  of  the  ground.  This  is  a  climatic  or  seasonal  effect  and 
can  not  be  controlled.  Trees  on  wet  ground  usually  show  the  trouble 
worst.     This  is  especially  true  with  young  trees  which  have  been  planted 

too  deeply. 

Die-Back. 

Cherry  trees,  while  not  attacked  by  many  fungus  diseases  in  Cali- 
fornia, are  very  subject  to  injury  from  unfavorable  conditions  of  soil, 
moisture,  etc.  As  a  result  of  such  injuries  the  trees  frequently  die 
back  from  the  top  and  suffer  severely  in  this  way. 

This  trouble  can  be  controlled  only  by  planting  on  soil  which  is  partic- 
ularly suited  to  the  cherry  and  by  determining  the  best  root  stock  for 
any  given  type  of  soil  or  locality. 

Trees  in  which  die-back  and  gummosis  are  produced  by  unusual 
climatic  conditions  should  be  cut  back  in  the  top  to  sound  wood,  and 
have  the  trunks  protected  from  sun  burn  by  whitewash  or  wrapping. 


Fruit  Drop.     See  Almond. 

CHRYSANTHEMUM. 

Rust   (Puccinia  chrysanthemi) . 
Figure  40. 

A  true  red  rust  causing 
injury  to  the  growth  of  the 
plants  with  the  production 
of  powdery  spore  masses 
on  the  leaves.  Only  seri- 
ous with  us  when  the  plants 
do  not  receive  sufficient 
water.  Vigorously  grow- 
ing plants  which  are  well 
irrigated  do  not  suffer  from 
this  trouble. 

CORN. 

Smut  (Ustilago  may  Ms). 
Produces  large,  tumor- 
like swellings  on  the  ears, 
stalks  or  tassels.  These 
finally  break  and  discharge 
their  contents  in  the  form  of  a  black,  powdery  dust  which  is  chiefly  com- 
posed of  the  spores  of  the  fungus.     Not  seriously  abundant. 


Fig.    40. — Chrysanthemum  rust    {Puccinia   chry- 
santhemi). 


"Bulletin  218] 


CALIFORNIA    PLANT    DISEASES. 


1111 


Rust  (Puccinia  sorghi). 
A  powdery,  red  rust  on  the  leaves.     Not  serious. 

Mold    (Diplodia  zcw) . 
The  corn  becomes  moldy  and  covered  with  fungus  growth  in  the  ear. 
<Quite  common  in  this  State  on  moist  land.     Affected  ears  should  be 

destroyed. 

COTTON. 
Boll  Rot. 
The  seed  and  a  part  of  the  lint  are  affected  with  a  soft  decay  while  the 
bolls  are  still  green. 

Cause  unknown.     Possibly  bacterial.     Noticed  for  the  first  time  in 
Imperial  Valley  in  1910. 


Fig.  41. — Nematode  galls  on  cucumber  root. 

CUCUMBER. 

Mildew    (Erysiphe  cichoracearum) . 

A  white  fungus  growth  all  over  the  surface  of  the  leaves.     Not  serious. 

Stem  Rot    (Sclerotinia  libertiana). 
This  dry  rot  of  the  stem  and  root  has  been  found  on  plants  growing 
in  greenhouses.     Not  serious  except  under  such   circumstances.     Use 
fresh,  unaffected  soil. 


1112  UNIVERSITY   OF    CALIFORNIA EXPERIMENT    STATION. 

Root  Knot  (Nematode).     Figure  41. 
Causes  swellings  all  over  the  main  and  smaller  roots.     Found  only  in 
greenhouses.    See  page  1076. 
Control  as  in  Stem  Rot. 

Leaf  Spot   (Altcrnaria  hrassicw,  var.  nigresccns) . 

This  fungus  has  been  known  to  do  considerable  damage  in  a  few  cases, 
causing  large  dead  spots,  later  covered  with  the  black  fruiting  fungus. 
Not  important  as  yet. 
Can  be  controlled  with  Bordeaux  mixture. 

CURRANT. 

Mildew  (Sphaerothcca  mors-uvw) . 
A  white,  powdery  mildew  on  the  leaves  and  fruit. 
Dust  with  dry  sulphur  while  the  leaves  are  wet  with  dew,  if  treatment 
seems  necessary. 

DAHLIA. 

Mildew. 

A  white,  powdery  mildew  on  the  leaves.     Not  serious. 
Treatment  as  for  currant  mildew. 

DEWBERRY.     See  Blackberry. 


Fig.  42. — Fruit  rot  of  egg  plant  (Botrytis  vulgaris). 

EGG  PLANT. 

Rot  (Botrytis).     Figure  42. 

A  moldy  decay  of  the  fruit.     The  fungus  mentioned  has  a  grey, 
dusty  appearance.     Not  serious. 


Bulletin  218] 


CALIFORNIA    PLANT    DISEASES. 


1113 


Wilt — Stem  Rot   (Nectria  ipomocw). 
This  fungus  causes  a  dry  rot  of  the  stem  and  root.     Usually  occurs 
only  on  old  plants  in  which  the  stem  has  been  injured. 
Do  not  plant  in  affected  soil  if  the  trouble  is  serious. 

EUCALYPTUS. 
Damping  Off. 

Causes  great  losses  by  a  stem  rot  and  dying  of  the  young  plants  in 
the  seed  bed. 

Sow  the  seed  in  clear  sand,  transplanting  to  better  soil  as  soon  as  the 
seedlings  are  large  enough  to  handle.  Keep  as  dry  as  possible  without 
checking  the  growth  seriously. 


Fig.  43. — Crown  gall  of  eucalyptus. 

Water  only  in  the  morning  and  as  little  as  possible  on  cloudy  days. 

Mildew. 
A  powdery  mildew  has  been  known  to  occur  on  seedlings,  but  is  not 
of  general  occurrence. 

Treat  with  dry  sulphur  as  for  other  mildews,  after  destroying  badly 
affected  plants.  Observe  precautions  as  for  damping  off  with  regard 
to  water. 

Leaf  Spot    (Hcndersonia  sp.). 
Sometimes  seen  on  the  blue  gum  (Eu.  globulus),  causing  dead  spots 
on  the  leaves.     Not  serious. 


1114 


UNIVERSITY   OF    CALIFORNIA — EXPERIMENT    STATION. 


Crown  Gall.     Figure  43. 
The  seedlings  of  some  species  frequently  develop  gall-like  swellings 
on  the  stem  near  the  surface  of  the  ground.     This  condition  does  not 
seem  to  be  particularly  injurious.    Cause  unknown.    Possibly  a  normal 
condition.  GRApE 

Mildew   (Uncinula  spiralis).     Figure  44. 

A  white  powdery  mildew  on  the  leaves  and  fruit  clusters. 
Dust  thoroughly  with  flowers  of  sulphur  in  moist  weather  before  the 
fungus  develops  extensively.     See  Bulletin  186,  California  Experiment 


Fig.  44. — Powdery  mildew  of  grape  (Uncinula  spiralis). 

Station.     On  account  of  the  importance  of  this  disease,  we  quote  as 
follows  from  California  Experiment  Station  Bulletin  197 : 

' '  The  most  common  mistake  of  those  who  have  attempted  to  follow  the 
directions  of  the  bulletin  (186)  has  been  a  failure  to  treat  the  vines 
thoroughly  or  rapidly  enough  in  the  beginning  of  the  season.  It  can 
not  be  too  strongly  urged  that  the  most  effective  way  to  control  the 
mildew  is  by  a  thorough  and  effective  sulfuring  in  the  beginning  of  the 
season.     This  alone  will  in  most  parts  of  the  State  keep  the  vines  free,. 


Bulletin  218] 


CALIFORNIA   PLANT    DISEASES. 


1115 


and  the  sulfuring  during  the  blossoming  is  needed  only  for  its  effect  on 
the  setting  of  the  fruit,  and  as  an  extra  precaution.  Sulfuring  later,  if 
needed,  is  a  proof  that  the  first 
two  have  not  been  well  done. 
This  is  true  for  the  whole  of 
the  two  central  valleys  and 
for  most  of  California,  except 
the  coast  belt  subject  to  sum- 
mer ocean  fog. 

"Definition  of  a  Thorough 
and  Effective  First  Sulfuring. 
— The  first  sulfuring  should 
be  made  when  the  shoots  are 
between  6  and  15  inches  long. 
It  should  be  done  in  such  a 
way  that  every  part  of  every 
leaf  of  every  vine  in  all  parts 
of  the  vineyard  receives  some 
sulfur,  and  the  whole  vine- 
yard should  be  gone  over  in 
as  short  a  time  as  possible. 
This  will  be  a  thorough  sul- 
furing. To  be  effective,  it 
must  be  followed  immediately 
by  two  or  three  days  of  warm 
weather.  Unless  this  happens, 
the  sulfuring  should  be  re- 
peated as  many  times  as  are 
necessary  until  the  proper 
weather  conditions  are  ob- 
tained. ' ' 

Black  Knot.  Figure  45. 
(California  Experiment 
Station  Bulletin  197)  :  "This 
is  one  of  the  commonest  and 
most  widely  distributed  dis- 
eases of  the  vine  in  California. 
Many  specimens  are  received  by  the  Experiment  Station  every  year, 
from  nearly  all  vine-growing  sections.  It  consists  of  peculiar  growths, 
or  swellings,  usually  near  the  surface  of  the  ground  on  the  upper  parts 
of  the  roots  or  the  lower  part  of  the  trunk.  It  often  occurs,  also,  on  all 
parts  of  the  trunk  and  branches,  but  only  rarely  on  the  canes. 

'As  a  rule  it  does  little  damage  unless  it  occurs  on  young  vines,  or 
attacks  old  vines  very  severely.    Figure  45  is  a  photograph  of  a  young 


Pig.   45. 


-Black  knot  of  grape    (Bacterium 
tumefaciens) . 


1116 


UNIVERSITY   OF    CALIFORNIA EXPERIMENT    STATION. 


vine  very  badly  attacked,  showing  a  large  mass  of  knots  at  the  surface 
of  the  ground,  and  four  on  the  stem  above  the  surface.  Such  a  vine  is 
almost  girdled  and  could  never  develop  into  a  healthy  plant.  In  some 
cases  where  the  knots  occur  on  a  branch  or  arm  they  could  be  removed 
and  the  vine  might  recover  perfectly. 

"It  is  not  uncommon  to  find  vines  with  large  masses  of  knots  on  all 
sides  of  the  trunk  and  on  all  the  arms,  which  yet  make  a  vigorous 
growth  and  produce  good  crops.     When  the  knots  extend  all  around 

the  trunk  of  an  old  vine, 
however,  it  may  be  girdled, 
and,  while  it  seldom  dies,  it 
may  become  weak  and  worth- 
less. 

' '  Various  theories  have 
been  advanced  as  to  the 
cause  of  this  disease,  but  the 
most  commonly  accepted  is 
that  it  is  due  to  abrupt 
changes  of  temperature,  and 
especially  to  autumn  frost 
occurring  before  the  vine 
has  become  thoroughly  dor- 
mant. This  cause  alone, 
however,  does  not  seem  to  be 
sufficient  to  cause  the  dis- 
ease. The  knots  appear  only 
on  vines  growing  in  moist 
places,  and  especially  in 
sandy  soil  in  the  hotter  re- 


gions 


# 


' '  Anything  which  causes 
a  vine  to  grow  vigorously 
late  in  the  season  and  pre- 
vents the  proper  ripening  of 
the  wood,  renders  it  suscep- 
tible to  the  disease. 

' '  In  accordance  with  these 
ideas,  the  remedies  advo- 
cated aim  at  causing  the  vine 
to  ripen  its  wood  early  and 
fig.  46.— couiure  disease  of  the  vine.  completely.    These  remedies 

are  drainage  of  the  soil,  fertilization  with  phosphatic  manures,  longer 
pruning,  raising  the  trunk  of  the  vine,  and  removal  of  the  knots.  Swab- 
bing with  lime,  sulfate  of  iron,  and  other  antiseptics  has  proven  useless. ' ' 

*It  is  now  known  to  be  due  to  an  infection  by  the  crown  gall  organism,  Bacterium 
tumefaciens. 


Bulletin  218]  CALIFORNIA  PLANT  DISEASES.  1117 

COULURE  OF  MUSCATS.     Figure  46. 

(California  Experiment  Station  Bulletin  197):  "The  Muscat  of 
Alexandria,  from  which  the  bulk  of  our  raisins  is  made,  has  a  tendency 
to  drop  its  blossoms  without  setting.  This  trouble  is  usually  known  in 
California  by  the  French  term  of  'coulure,'  which  may  be  translated 
'dropping.'  The  first  crop  is  particularly  subject  to  this  defect,  which 
is  often  so  serious  that  a  large  part  and  sometimes  the  whole  of  the  first 
crop  is  lost." 

This  trouble  is  due  to  a  failure  of  pollination  of  the  blossom.  The 
author  recommends  as  a  remedy  planting  occasional  rows  of  other 
varieties  with  the  Muscat.  For  this  purpose  the  Palomino,  Perruno, 
Beba  and  Berger  are  suggested. 

MISCELLANEOUS  DISEASES. 

The  grape  is  affected  in  California  by  several  miscellaneous  and 
peculiar  diseases,  most  of  which  are  not  very  clearly  defined.  Some  of 
these  have  received  the  names  Anaheim  Disease,  Red  Leaf,  Little  Leaf 
and  other  local  names. 

The  first  named,  also  called  the  California  Vine  Disease,  was  of  the 
greatest  importance  a  number  of  years  ago  when  almost  all  the  vine- 
yards in  southern  California  died  from  a  mysterious  trouble  which 
received  this  name.  Although  carefully  investigated  at  the  time  by 
Professor  Newton  B.  Pierce,  at  that  time  of  the  United  States  Depart- 
ment of  Agriculture,  no  definite  cause  of  this  disease  was  ever  discovered. 
At  present  vines  are  occasionally  affected  with  something  which  might 
pass  for  the  same  disease,  but  it  is  difficult  or  impossible  even  for  the 
experienced  plant  pathologist,  save,  perhaps,  one  who  was  familiar  with 
the  Anaheim  disease  at  the  time  of  its  first  and  greatest  period  of  preva- 
lence, to  say  just  what  is  really  Anaheim  disease  and  what  is  one  of  the 
various  troubles  which  have  received  other  names.  So  little  is  under- 
stood about  these  vine  diseases  at  present  that  it  is  scarely  worth  while 
to  attempt  to  discuss  them  in  a  publication  of  this  sort.  We  quote  as 
follows  from  California  Experiment  Station  bulletin  197: 

Mysterious  Dying  of  Vines  (Anaheim  Disease). — The  vine,  like  most  plants, 
especially  fruit  trees,  which  are  cultivated  on  a  large  scale,  is  subject  to  diseases  of 
more  or  less  intensity  whose  cause  is  not  thoroughly  understood.  These  diseases  are 
(1)  caused  by  parasitic  organisms  which  have  so  far  escaped  detection,  or  (2)  what 
is  usually  known  as  "physiological." 

Physiological  diseases  are  presumably  due  to  some  unfavorable  conditions.  For 
example,  chlorosis,  or  the  failure  of  the  leaves  to  develop  chlorophyll  properly,  is  due 
to  an  excess  of  soluble  lime  carbonate  in  the  soil,  and  is  intensified  by  cold,  dampness 
and  the  susceptibility  of  the  variety. 

The  most  serious  of  these  two  classes  of  diseases,  which  affects  the  vines,  is  the 
Anaheim,  or,  as  it  is  sometimes  called,  the  California  Vine  Disease.  Notwithstand- 
ing that  it  has  been  the  subject  of  continuous  investigation  for  over  fifteen  years  its 
cause  is  still  quite  obscure.  Even  the  characterization  and  detection  of  the  disease 
are  so  uncertain  that  vineyards,  which  after  several  years  of  observation  by  the  most 

6_Bul.  218 


1118  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION. 

experienced  investigators  have  been  pronounced  infected,  have  later  been  declared 
free.  This  has  led  to  such  a  diversity  of  opinion  that  while  one  expert  claims  that 
the  disease  exists  in  every  vineyard  in  the  State,  another  would  have  us  believe  that 
no  such  disease  exists  at  all,  and  that  all  cases  of  dying  vines  can  be  ascribed  to  one 
or  other  of  the  recognized  vine  diseases. 

Neither  of  these  extreme  views  seems  to  explain  completely  the  observed  facts. 
While  many  cases  of  supposed  Anaheim  have  proved  to  be  nothing  but  Phylloxera, 
root-rot,  vine-hopper,  drought,  etc.,  there  still  remain  a  large  number  of  unexplained 
cases. 

In  some  cases  the  symptoms  are  practically  identical  with  those  of  some  of  the 
"physiological"  diseases  which  affect  the  vine  in  Europe.  Typical  cases  of  Rougeot 
have  been  noted  in  Contra  Costa  County,  of  Brunissurc  in  San  Joaquin,  and  of 
Folletage  in  Fresno,  Kings,  and  other  counties.  In  Sonoma  County  the  disease  of 
Red-leaf,  which  has  some  analogy  with  Anaheim,  has  been  studied  by  Mr.  O.  Butler. 
An  account  of  these  diseases  may  be  found  in  Bulletin  168,  entitled  "Observations 
on  Some  Vine  Diseases  in  Sonoma  County." 

In  a  general  way,  as  these  troubles  are  due  to  soil  and  climatic  conditions  which 
weaken  the  vine,  they  are  to  be  combated  by  cultural  methods  which  tend  to  invigor- 
ate. Shorter  pruning,  thorough  cultivation,  irrigation  or  drainage,  and  fertilization 
will  in  most  cases  be  effective  in  curing  vines  which  are  not  too  far  gone. 

Many  cases  have  been  brought  to  the  attention  of  the  station  during  the  last  two 
years,  in  which  vines  which  were  apparently  healthy  the  previous  year  have  failed 
to  bud  out  in  the  spring,  or  budded  out  weakly  and  very  late.  The  cause,  in  most 
cases,  seemed  to  be  some  injury  to  the  vines  during  the  growing  season  of  the  pre- 
vious year.  This  cause  was  in  many  cases  the  attacks  of  vine-hoppers.  Black 
Prince  vines  growing  in  Tokay  vineyards  have  very  often  been  killed.  This  seems 
to  be  because  the  vine-hoppers,  having  a  special  fondness  for  this  variety,  congre- 
gate in  large  numbers  on  such  isolated  vines.  Whenever  the  hoppers  are  sufficiently 
abundant  to  cause  the  dropping  of  the  leaves  in  summer,  the  vine  fails  to  ripen  its 
wood  properly.  Without  mature  green  leaves  the  buds  and  canes  do  not  receive  the 
stores  of  starch  which  they  need  for  the  new  growth  in  spring,  and  will  either  grow 
poorly  the  following  year  or  fail  to  start  at  all. 

When  a  new  growth  of  leaves  in  autumn  follows  summer  defoliation  by  hoppers, 
mildew,  or  other  causes,  the  effect  is  even  worse.  The  new  shoots  which  start 
exhaust  what  food  reserves  the  vine  possesses,  and  the  leaves  are  killed  by  the  early 
winter  frosts  before  they  have  been  able  to  return  the  supplies  they  have  taken  from 
the  canes.  Similar,  but  less  severe,  effects  have  been  observed  following  a  bad  attack 
of  mildew. 

This  starvation  of  the  canes  and  buds  may  be  brought  about  in  another  way, 
namely,  by  the  production  of  too  large  a  crop.  It  is  often  possible,  by  excessively 
long  pruning,  to  cause  a  vine  to  produce  an  abnormally  large  crop  of  grapes.  The 
larger  the  crop  the  more  material  it  takes  from  the  vine,  and  if  too  large,  the  vine 
is  unable  to  support  it  and  at  the  same  time  lay  up  reserve  materials  in  its  canes 
and  buds.  In  consequence,  an  extra  large  crop  is  often  followed  by  weak  growth 
in  the  spring,  and  a  consequent  small  crop  the  following  autumn.  Vines  of  heavy 
bearing  varieties  may  even  be  killed  in  this  way,  by  repeated  long  pruning. 

This  fact  has  been  long  recognized  by  practical  grape-growers.  Lately,  Professor 
L.  Ravaz,*  of  the  National  School  of  Agriculture  at  Montpellier,  France,  has 
advanced  the  opinion  that  the  death  of  vines,  as  a  consequence  of  overbearing,  is 
much  commoner  than  is  usually  supposed.  This  overbearing  may  occur  as  a  conse- 
quence of  various  conditions  other  than  long  pruning.  Some  seasons  are  peculiarly 
favorable  to  heavy  crops.  Certain  diseases  and  injuries  induce  temporary  heavy 
bearing.  Whatever  the  cause  of  abnormally  heavy  crops,  Professor  Ravaz  believes 
that  they  may  result  in  the  death  of  vines.  This  is  the  explanation  he  gives  of  the 
death  of  large  numbers  of  vines  in  southern  France,  Algeria,  and  other  countries, 
and  he  ascribes  our  so-called  Anaheim  disease  to  the  same  cause. 

This  is  substantially  the  explanation  given  of  the  dying  of  vines  in  Santa  Clara, 

*  "Influence  de  la  surproduction  sur  la  Vegetation  de  la  Vigne,"  by  L.  Ravaz,  Coulet 
et  fils,  Montpellier,  1906. 


Bulletin  218] 


CALIFORNIA   PLANT    DISEASES. 


1119 


in  Bulletin  134,  which  was  published  before  the  region  was  declared  infested  by 
Anaheim  disease.  Whether  this  explanation  is  sufficient  is  still  doubtful,  though 
it  is  rendered  probable  by  the  fact  that  healthy  young  vineyards  are  now  growing 
in  Santa  Clara,  on  the  same  soil  where  vines  have  been  killed  by  Anaheim  disease. 

GRAPE  FRUIT.     See  Orange. 
GUAVA. 

RUSSETING. 

In  this  trouble  the  surface  of  the  fruit  shows  a  scabby  condition  indi- 
cated by  the  above  name.     Thought  to  be  caused  by  an  insect. 


Fig  47. — Rust  of  hollyhock  (Puccinia  malv  ace  arum) . 

HOLLYHOCK. 
Rust  {Puccinia  malvacearum) .  Figure  47. 
In  this  disease  the  fungus  injures  the  leaves  seriously,  becoming  visible 
in  the  form  of  numerous  small  pustules  of  spores  on  the  under  side. 
These  pustules  are  dense  and  compact  rather  than  dusty  as  in  most  rusts. 
The  wild  mallows  are  affected  with  the  same  fungus.  Hollyhocks  grown 
in  rich  soil  with  an  abundance  of  water  are  much  less  affected  than  those 
which  lack  moisture. 


1120 


UNIVERSITY   OF    CALIFORNIA — EXPERIMENT    STATION. 


Fig.  48. — Leaf  spot  of  iris  (Hetero- 
sporium  gracile). 


Irrigating  and  fertilizing  abundantly  will  control  this  disease. 
Spraying  with  Bordeaux  mixture  and  other  fungicides  is  sometimes 
resorted  to,  but  this  treatment  is  not  very  satisfactory. 

IRIS. 

Leaf  Spot    (Ilctcrosporium  gracile).     Figure  48. 

Large,  elliptical  dead  spots  appear 
on  the  leaves,  with  a  yellow  margin 
between  the  dead  and  the  green  tissue. 

Quite  disfiguring,  but  no  treatment 
ordinarily  considered  necessary. 

LEMON. 

Gummosis.     Figure  49. 

Characterized  by  the  exudation  of 
gum  from  the  trunk  of  the  tree  just 
above  the  point  of  budding.  The  tree 
appears  yellow  and  dies  when  badly 
affected.  Occurs  on  poorly  drained, 
heavy  soil,  especially  if  the  point  of 
budding  is  deeply  covered  with  earth 
and  where  the  soil  about  the  trunk 
is  undisturbed  by  cultivation.  This 
trouble  is  more  common  on  lemons  than  on  oranges. 

Gumming  is  a  characteristic  of  the  citrus  tree  when  affected  by  any 
injurious  condition.  Frequently,  for  instance,  when  trees  have  been 
extremely  dry  and  suffering  from  a  lack  of  moisture  gum  will  break  out 
at  the  crotches  or  twig  axils  when  an  abundant  supply  of  water  is 
furnished.  If  the  twigs  in  this  or  any  other  manner  are  caused  to  die 
back  for  a  short  distance  gum  is  very  likely  to  exude  after  irrigation 
at  the  point  where  the  dead  portions  of  the  twig  join  the  live  tissue. 
Any  injury  or  irritation  may  have  the  same  effect.  When  citrus  trees 
are  budded,  either  in  the  nursery  or  in  the  case  of  orchard  trees,  gum- 
ming often  occurs  at  the  point  of  budding,  particularly  if  a  large  supply 
of  moisture  is  furnished  soon  after  the  budding  is  done.  Many  buds 
are  often  killed  in  this  way  as  a  result  of  rain  or  irrigation.  Such  effects 
as  these  are  not  usually  very  serious,  except  that  in  the  case  of  budding 
the  process  may  have  to  be  repeated. 

Orange  or  lemon  nursery  trees  one  or  two  years  of  age  sometimes  gum 
badly  just  above  the  point  of  budding  from  no  very  apparent  cause.  As 
a  result  of  such  gumming  the  cambium  layer  is  killed  and  if  the  injury 
is  extensive  the  tree  may  die.  In  the  majority  of  cases,  however,  if  the 
trees  are  affected  on  only  one  side  and  planted  and  cared  for  properly, 
they  make  a  complete  recovery  and  after  a  year  or  two  the  injury  disap- 


Bulletin  218] 


CALIFORNIA   PLANT    DISEASES. 


1121 


pears.  These  cases  probably  start  in  the  majority  of  instances  from  an 
excessive  flooding  of  the  soil  with  water,  put  on  either  while  the  trees 
are  growing  to  force  them  along  or  just  before  they  are  dug  in  order 
to  assist  the  operation  of  " balling."  Trees  affected  in  this  way  when 
received  for  planting  should  not  be  looked  upon  as  having  any  serious 
contagious  disease,  but  the  buyer  should  simply  discard  those  in  which 


Fig.  49. — Gum  disease  of  lemon. 

the  inner  bark  is  badly  affected  and  notify  the  nurseryman  of  the  num- 
ber of  trees  found  in  this  condition.  If  the  trees  have  once  been  planted 
and  then  die  or  fail  to  grow  it  is  impossible  to  decide  whether  the  gum- 
ming took  place  before  or  after  the  trees  were  planted. 

In  order  to  successfully  control  gum  disease  in  orchard  trees,  soil  con- 
ditions must  first  of  all  be  improved  by  securing  drainage,  removing 


1122  UNIVERSITY   OF    CALIFORNIA — EXPERIMENT    STATION. 

soil  from  about  the  bud  and  thoroughly  cultivating  or  digging  about 
the  tree.  Water  must  not  be  allowed  to  stand  about  the  trunk  or  the  soil 
remain  continually  saturated.  After  thus  improving  conditions,  the  tree 
itself  may  be  treated  by  taking  out  narrow  slits  of  bark  on  several  sides 
of  the  trunk,  extending  from  the  ground  up  to  the  fork.  These  slits 
should  pass  through  the  gummy  portion  and  also  the  unaffected  bark. 
This  will  usually  suffice  to  effect  a  cure  if  taken  in  time  and  if  soil  con- 
ditions are  sufficiently  improved. 
For  further  treatment  see  Bulletin  200,  California  Experiment  Station. 

Brown  Rot   (Pythiacystis  citrophthora) .     Figure  50. 
A  very  virulent  form  of  decay  spreading  rapidly  through  the  boxes 
from  fruit  to  fruit.     Affected  specimens  show  a  brown,  rather  dry  decay 


Fig.   50. — Brown  rot  of  lemon    (Pythiacystis  citrophthora). 

of  the  rind  upon  which  a  delicate,  scanty  white  mold  develops  when 
considerable  moisture  is  present.  Fruit  out  in  the  open  shows  no  mold 
on  the  surface.  Affected  fruit  has  a  peculiar  odor  which  is  very  char- 
acteristic. Mostly  seen  in  lemons  held  in  storage  for  curing.  In  wet 
weather  this  decay  often  appears  on  the  fruit  while  still  on  the  tree,  but 
it  is  mostly  confined  to  that  within  two  feet  of  the  ground.  The  disease 
affects  all  kinds  of  citrus  fruit  in  this  manner. 

The  fungus  which  causes  this  trouble  is  primarily  a  soil  inhabitant, 
living  naturally  in  the  ground  beneath  the  trees  where  its  spores  are 
produced. 

Orchard  infection  is  prevented  by  keeping  the  trees  pruned  up  some- 
what from  the  ground,  cultivating  the  soil  under  the  trees  in  summer 
and  covering  it  in  winter  with  straw  or  a  green  cover  crop.  Spraying 
the  ground  under  the  trees  in  winter  with  thick  Bordeaux  mixture  is 
also  helpful.     The  worst  infection,  that  of  lemons  in  storage,  is  con- 


Bulletin  218] 


CALIFORNIA   PLANT   DISEASES. 


1123 


tracted  in  the  tank  of  the  washing  machine  where  the  water  becomes 
extremely  infectious  from  the  presence  of  spores  brought  in  with  the 
orchard  soil  and  dust.  This  is  easily  controlled  by  disinfection  of  the 
wash  water  with  copper  sulphate. 

See  Bulletin  190,  California  Experiment  Station. 

Cottony  Mold — White  Rot  (Sclerotinia  libertiana).     Figure  51. 
Causes  decay  of  the  fruit  in  the  curing  house  with  the  production  of 
an  abundant  white  mold  spreading  over  the  lemons.     In  this  mold 


Fig.  51. — Cottony  mold  of  lemon   {Sclerotinia  libertiana). 

are  found  irregularly-shaped,  black,  seed-like  bodies  called  sclerotia 
from  which  another  stage  of  the  fungus  develops.  The  same  fungus 
also  develops  in  the  orchard  soil  during  the  rainy  season  and  often 
becomes  very  abundant  upon  green-manure  crops  or  other  vegetation 
growing  about  the  lemon  trees,  particularly  upon  the  vetch.  The 
sclerotia  develop  upon  green-manure  crops  or  directly  upon  the  soil, 
the  latter  during  the  rainy  season,  and  out  of  them  grow  little  funnel- 
shaped  toadstool-like  bodies  which  give  off  the  spores  of  the  fungus. 


1124 


UNIVERSITY   OP    CALIFORNIA EXPERIMENT    STATION. 


The  fungus  is  not  actively  parasitic  and  it  has  been  found  difficult 
to  infect  lemons  with  its  spores  save  when  they  are  injured  or  bruised 
in  some  way.  They  also  require  considerable  moisture  for  infection. 
Experiments  have  shown  that  almost  all  the  infection  takes  place  at 
the  stem  end  of  the  lemon  where  it  is  cut  from  the  tree,  and  practically 
all,  it  is  probable,  in  the  washing  water,  except  in  the  case  of  fruit 
allowed  to  stand  out  in  the  rain  for  some  time,  when  infection  may  take 
place. 

Cottony  mold  sometimes  develops  to  a  considerable  extent  in  packing 
houses  where  the  fruit  is  being  washed  in  bluestone  solution  to  prevent 
brown  rot,  from  which  fact  it  appears  that  a  strength  of  this  substance 

which  kills  brown  rot 
spores  does  not  kill  those 
of  the  cottony  fungus. 
Laboratory  tests  have 
shown  this  to  be  a  fact. 
The  control  of  cottony  rot, 
therefore,  depends  upon 
either  using  the  germicide 
stronger  than  that  used 
for  brown  rot  or  finding 
means  for  preventing  the 
development  of  the  fun- 
gus in  the  orchard.  Along 
the  former  line  we  may 
say  that  it  is  not  safe  to 
use  bluestone  in  the  wash 
water  much  stronger  than 
it  is  now  being  used  in 
many  houses  for  brown  rot  control ;  a  strength  of  1/50  of  one  per  cent, 
or  about  1J  pounds  of  bluestone  to  1,000  gallons  of  water.  This  would 
mean  putting  in  about  the  quantity  of  bluestone  stated  into  a  1,000- 
gallon  tank  in  the  morning  and  fortifying  this  with  about  one  pound 
more  in  the  afternoon,  after  considerable  wash  water  has  entered  the 
tank.  The  question  of  the  strength  of  bluestone  in  lemon  wash  water 
depends  to  a  large  extent  upon  the  quality  of  the  water  used  as  to  its 
alkali  content,  since  the  alkali  salts  neutralize  the  copper  sulphate. 
This  whole  question  of  disinfecting  lemon  wash  water  is  now  being 
investigated  at  the  Whittier  Laboratory. 

In  regard  to  orchard  control  of  this  trouble,  we  may  say  that  the  cot- 
tony mold  has  had  a  very  marked  prevalence  since  the  use  of  vetch  as 
an  orchard  cover  crop  became  so  general.  There  is  much  ground  for 
believing  that  these   facts  are  related  to   one  another,  cottony  mold 


Fig.    52. — Peziza    developing    from    sclerotium    of 
cottony  mold  fungus  (Sclerotinia  libertiana). 


Bulletin  218] 


CALIFORNIA   PLANT   DISEASES. 


1125 


having  become  more  abundant  on  account  of  the  opportunity  given  for 
its  development  in  the  orchard  by  the  presence  of  the  vetch  plant,  upon 
which  it  develops  particularly  well.  We  are  by  no  means  ready  to 
advocate  the  discontinuance  of  cover  crop  practice  in  lemon  groves  for 
this  one  reason,  although  it  may  be  said  that  other  factors  are  develop- 
ing in  actual  practice  which  make  the  growth  of  such  a  crop  in  a  lemon 


Pig.   53. — Peziza  of  cottony  mold  fungus  growing  in  orchard  soil. 

grove  undesirable  from  some  other  point  of  view.     This  whole  subject 
is  now  under  investigation  and  will  be  reported  on  in  a  future  bulletin. 
See  Bulletin  190,  California  Experiment  Station. 

Gray  Mold  {Botrytis  vulgaris). 

This  produces  a  dark  colored  decay  of  the  rind  on  which  a  dirty  gray 
mold  develops.  The  fungus  is  able  to  develop  at  low  temperatures  close 
to  the  freezing  point  and  sometimes  causes  considerable  loss  in  fruit  held 
in  cold  storage.     Not  ordinarily  very  serious. 


1126 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION. 


Blue  and  Green  Mold  (Penicillium  italicum  and  P.  digitatum).     See  Orange. 

Twig   Blight    (Sclerotinia  .lioertiana) . 

The  twigs  die  back  from  the  tip  in  moist  weather,  showing  to  some 
extent  a  white  moldy  fungus  upon  the  surface  in  which  may  be  imbedded 
small,  hard,  seed-like  bodies  or  sclerotia,  at  first  white  but  finally  becom- 


Fig.  54. — Green  and  blue  mold  rot  of  lemon   (Penicillium  digitatum  and  italicum). 

ing  black.  A  mass  of  gum  exudes  at  this  point.  This  fungus,  which  is 
the  same  as  that  causing  the  cottony  mold,  occasionally  infects  the  tree 
itself,  both  with  lemons  and  other  citrus  trees,  with  the  effect  just 


Fig.    55. — Supposed   effect   of  wither-tip    fungus   on   lemon   fruit    (Colletotrichum 

gloeosporioides) . 

described.  The  infection  comes  from  spores  produced  by  the  growth  of 
the  fungus  upon  the  green  manure  crop.  Not  serious.  This  effect  is 
sometimes  confused  with  that  of  the  next  described  disease. 


Bulletin  218]  CALIFORNIA  PLANT  DISEASES.  1127 

Wither-Tip,  "Tear  Stain"    (Colletotrichum  gloeosporioides) .     Figures  55  and  56. 

The  effects  of  this  disease  consist  in  a  general  way  in  a  spotting  of  the 
fruit  and  leaves  and  killing  back  of  the  twigs,  and  an  attack  upon  the 
young,  newly-formed  fruit,  causing  it  to  drop.  To  what  extent,  how- 
ever, such  effects  occur  in  California  solely  from  the  attacks  of  this 
fungus,  without  the  aid  of  other  harmful  conditions,  is  somewhat  doubt- 
ful and  difficult  to  determine.  Wither-tip  is  a  trouble  of  quite  common 
occurrence  in  Florida  and  probably  most  other  citrus  growing  regions. 
It  has  been  known  to  exist  in  California  for  some  time  but  there  has 
always  been  a  question  as  to  how  much  this  fungus  is  really  parasitic 
and  how  much  it  develops  simply  in  a  secondary  manner  upon  tissues 
injured  in  other  ways.  Little  attention  was  given  to  the  subject  in 
California  until  the  winter  of  1908-09,  when  there  appeared  to  be  a 
considerable  epidemic  of  wither-tip  in  southern  California,  particularly 
on  lemons  and  grape  fruit.  Since  that  time  the  subject  has  received 
considerable  investigation. 

The  most  pronounced  effect  upon  lemons  attributed  to  the  wither-tip 
fungus  has  been  a  slight  spotting  of  the  fruit,  the  spots  being  quite 
numerous  upon  the  exposed  side  of  the  lemons  while  still  on  the  tree, 
each  spot  of  small  size  and  reddish  color.  Such  spotting  has  been  quite 
generally  attributed  to  this  fungus  and  yet  it  may  be  said  that  in 
numerous  efforts  made  to  produce  such  an  effect  by  direct  infection 
with  the  spores  of  the  wither-tip  fungus,  entire  failure  has  always  been 
the  result.  The  same  is  true  in  regard  to  the  dropping  of  young  fruit. 
It  has  frequently  been  assumed  that  this  is  an  effect  of  the  wither-tip 
fungus,  yet  efforts  made  to  produce  the  same  effect  by  spraying  young 
lemons  profusely  with  wither-tip  spores  have  always  failed  to  produce 
infection  or  cause  such  fruit  to  drop  any  more  than  that  which  was  not 
sprayed. 

The  fungus  commonly  shows  itself  to  the  eye  in  the  form  of  numerous 
minute  black  dots  upon  the  surface  of  dead  twig  tips  or  on  dead  spots 
on  the  leaf.  In  the  latter  case,  starting  on  spots  killed  by  fumigation, 
fire  or  other  injuries,  or  possibly  without  preliminary  injury  on  old, 
nearly  dead  leaves,  the  spots  slowly  spread  in  an  oval  form,  with  a  yellow 
band  between  the  dead  and  green  tissue  and  the  characteristic  black  dots 
(pycnidia)  upon  the  surface  of  the  dead  portion. 

Another  fungus,  a  species  of  Pleospora,  having  a  similar  appearance 
and  effect,  has  also  been  found  quite  abundantly  on  citrus  trees  in  the 
northern  part  of  the  State. 

The  wither-tip  fungus  is  one  of  the  commonest  inhabitants  of  our 
citrus  trees.  Every  dead  twig,  every  fallen  leaf,  every  leaf  or  twig 
injured  by  fire  or  any  other  cause,  immediately  becomes  covered  with  a 
flourishing  growth  of  this  fungus.  Young  lemons  which  fall  to  the 
ground  from  any  cause  show  the  same  fungus  upon  them  after  a  short 


1128 


UNIVERSITY   OF    CALIFORNIA — EXPERIMENT    STATION. 


time.  It  has  even  been  found  that  the  most  healthy,  green  leaves,  if 
picked  from  the  tree  and  placed  in  a  moist  chamber,  soon  become  cov- 
ered with  this  wither-tip  fungus.  Trees  suffering  from  gum  disease, 
gophers,  drouth  or  any  other  influence  which  causes  them  to  lose  their 
vitality  and  begin  to  weaken  and  die  back  in  the  branches  soon  develop 
an  abundance  of  this  organism.  It  is  also  likely  that  citrus  insects, 
like  the  red  spider  and  any  other  which  punctures  or  injures  the  fruit, 
may  promote  the  development  of  this  fungus. 

All  in  all,  our  conclusion  has  been  that  it  is  extremely   doubtful 
whether  the  wither-tip  fungus  ever  in  California  attacks  sound,  unin- 


Fig.   56. — Effect  of  wither-tip  fungus  on  sickly  lemon  leaf  and  twig    (Col- 

letotrichum  gloeosporioides) . 

jured,  vigorous  foliage,  twigs  or  fruit,  or  develops  at  all,  save  in  a 
secondary  manner  or  following  some  other  injury.  The  subject  is  still 
receiving  careful  investigation  and  will  be  made  the  subject  of  a  future 
bulletin. 

"Within  the  last  two  or  three  years  considerable  spraying  has  been 
done  in  lemon  groves  in  southern  California  with  the  idea  of  combating 
the  supposed  effects  of  this  fungus.  Such  work  has  been  done  with 
Bordeaux  mixture  and  also  with  various  sulphur  sprays  made  by  com- 
bining sulphur  with  lime,  soda  or  potash.  Some  growers  have  believed 
that  they  saw  good  results  following  such  spraying,  while  others  were 
unable  to  see  such  benefits.     "We  are  following  the  results  of  such  work. 


Bulletin  218] 


CALIFORNIA   PLANT    DISEASES. 


1129 


Red  Rot.     Figure  57. 


A  curing-house  trouble  in  which  the  rind  develops  a  rusty  bronze  color 
and  gradually  dries  down  into  a  sunken  condition  with  a  dark  red  or 
black  color. 

Cause  unknown;  apparently  not  a  parasite. 


Fig.  57. — Red  rot  of  lemon. 


Fig.  58. — Peteca  of  lemon. 

Peteca.     Figure  58. 

This  trouble  shows  itself  in  the  form  of  deep  sunken  pits  in  the  rind 

of  the  lemon  after  it  has  been  in  the  curing  house  for  some  time.     The 

tissue  at  these  spots  is  found  to  be  dried  and  shrunken  prematurely. 


1130 


UNIVERSITY   OF    CALIFORNIA — EXPERIMENT    STATION. 


The  trouble  is  not  serious,  save  in  its  effect  upon  the  appearance  of  the 
fruit.     Cause  unknown. 

LETTUCE. 

Damping  Off   (Botrytis  vulgaris). 
Drop   (Sclcrotinia  libertiana) . 

The  plants  wilt  and  die,  collapsing  upon  the  ground.  The  stem  rots 
off  just  at  the  surface  of  the  ground  and  one  or  the  other  of  the  above 
named  fungi  is  usually  found  at  this  point.  Other  damping  off  fungi 
may  cause  the  trouble  in  some  instances. 

See  Tomato. 

LOGANBERRY.     See  Blackberry. 


Fig.  59. — Scab  of  loquat   (Fusicladium  eriobotryae) . 

LOQUAT. 
Scab    (Fusicladium  eriobotryce).     Figure  59. 

Similar  to  apple  and  pear  scab,  to  which  trees  this  is  related.     Affects 
both  fruit  and  leaves. 

Blight    (Bacillus  amylovorus) . 

The  blossoms  and  twigs  wither  and  die.     This  trouble  is  caused  by  the 
pear  blight  organism,  to  which  the  loquat  is  quite  susceptible. 
Same  treatment  as  for  pear  blight. 


MADRONE. 

Leaf  Spot   (Sphaerella  arbuticola) 

Produces  disfiguring  dead  spots  on  the  leaves. 


Bulletin  218] 


CALIFORNIA   PLANT   DISEASES. 


1131 


NURSERY  STOCK. 
Crown  Gall.     Figure  11. 
Very  common  on  the  roots  of  nursery  trees,  particularly  those  of  the 
stone  fruits.     See  Almond. 

Discard  affected  trees  and  never  use  such  for  planting.  Do  not  grow 
nursery  stock  on  affected  land. 

Root  Knot    {Nematode).     Figure  41. 
These  microscopic  worms  sometimes  invade  the  nursery,  producing 
galls  and  swellings  all  over  the  roots  of  the  young  trees. 
Destroy  affected  plants. 

Allow  infested  soil  to  dry  for  a  season  before  using  it  again. 
See  page  1076. 

OAT. 
Rust  ( Puccinia  graminis ) . 

Produces  numerous  pustules  of  the  black  or  red  rust  condition  on  the 
surface  of  the  plants,  sometimes  covering  the  leaves  with  the  reddish, 
powdery  spores.  Sometimes  abundant  in  wet  seasons,  badly  injuring 
the  crop. 

No  treatment  is  feasible  save  the  use  of  resistant  varieties. 

Smut  (Ustilago  avenw). 

Causes  the  heads  of  grain  to  turn  into  black,  dusty,  smutty  masses. 
May  be  entirely  pre- 
vented by  the  seed 
treatment  recom- 
mended for  barley 
smut. 

OLEANDER. 
Twig    Gall. 
( Tuberculosis ) .     Fig- 
ure 60. 

This  plant  is  some- 
times affected  with 
galls  or  swellings  on 
the  stems  and  twigs, 
very  similar  to  the 
olive  disease  of  the 
same  nature.  Ap- 
pears to  be  caused  by 
the  same  or  a  very 
similar  organism.  Not 
serious. 


Fig.  60. — Stem  gall  of  oleander. 


Leaf  Spot  (Macrosporium  nerium). 
Produces  dead  spots  on  the  leaves.     Not  important. 


1132 


UNIVERSITY   OF    CALIFORNIA — EXPERIMENT    STATION. 


OLIVE. 

Tuberculosis    (Bacterium   Savastanoi).     Figure  Gl. 

This  is  a  bacterial  disease,  the  parasitic  organism  causing  a  production 

•of  galls  of  considerable  size  on  the  trunk,  branches  and  small  twigs. 

Some  varieties  are  more  susceptible  than  others.     If  taken  in  time  the 


Fig.  61. — Tuberculosis  of  olive  (Bacterium  Savastanoi). 

disease  can  be  successfully  controlled  by  cutting  out  all  affected  parts 
and  saturating  the  wounds  with  a  strong  disinfectant. 
See  Bulletin  120,  California  Experiment  Station. 


Bulletin  218] 


CALIFORNIA  PLANT  DISEASES. 


1133 


Leaf   Spot    (Cycloconium   oleaginum) 
Causes  spots  of  considerable  size  on 

the   leaves.     No  treatment   is  usually 

necessary.     Dry  Rqt     Figure  62. 

Characterized  by  the  appearance  of 

numerous  large  spots  on  the  fruit  which 

dry  and  sink  in.    During  some  seasons 

the  olive  is  considerably  affected  with 

this  trouble.    Cause  not  known. 

Root  Rot  (Toadstool  disease).     See  Almond. 

ONION. 
Downy  Mildew   (Peronospora  schleideniana). 

Causes  serious  losses  some  years  in 
onions  grown  for  seed  during  the  win- 
ter. The  fungus  affects  the  seed  stalks 
and  leaves  with  the  production  of  large 
dead  areas  upon  which  may  be  seen  the 
dark,  purplish-colored  mildew.  The  seed 
stalks  topple  over  and  fail  to  develop 
seed. 

This  disease  has  not  been  successfully 
controlled  in  California,  but  in  Eastern 
states  has  yielded  fairly  well  to  spray- 
ing with  Bordeaux  mixture,  to  which  a 
resin  "sticker"  has  been  added.  This 
spraying  must  be  done  at  frequent  in- 
tervals, commencing  before  the  mildew 
appears. 

The  development  of  resistant  strains 
by  seed  selection  is  promising. 


Fig.  62. — Dry  rot  of  olive  fruit. 


ORANGE. 
In  the  consideration  of  diseases  of  the  orange  and  other  citrus  trees, 
it  is  desirable  to  mention  at  the  outset  certain  peculiar  characteristics  of 
such  trees  which  distinguish  them  to  a  considerable  extent  from  any 
other  cultivated  plant.  These  features  make  the  citrus  tree  specially 
liable  to  peculiar,  obscure  effects  of  climate,  soil  or  other  non-parasitic 
conditions,  and  in  making  an  investigation  of  citrus  diseases  one  should 
not  fail  to  keep  these  peculiarities  of  the  citrus  tree  prominently  in 
mind.  First,  is  the  very  free  circulation  of  water  from  the  roots  up  into 
the  tops,  which  occurs  when  plenty  of  moisture  is  available  in  the  soil. 
This  water  carries  with  it  all  the  food  materials  from  the  soil  which  the 
tree  takes  up  and  thus  we  see  that  the  citrus  tree  must  take  up  large 
7_Bul.  218 


1134  UNIVERSITY   OF    CALIFORNIA — EXPERIMENT   STATION. 

amounts  of  such  food  material  very  freely  when  large  amounts  of  soil 
moisture  are  available.  This  feature  is  of  no  special  importance  when 
the  trees  receive  a  uniformly  sufficient  supply  of  water,  but  must  have 
very  decided  effects  when  the  moisture  supply  is  irregular  and  the  soil 
becomes  alternately  ..very  wet  and  very  dry.  In  such  cases  the  soil  food 
materials  are  supplied  to  the  tree  in  a  correspondingly  irregular  manner. 

Connected  with  this  feature  is  the  second  peculiarity  which  we  would 
mention,  namely,  the  quickness  with  which  citrus  trees  respond  when 
needed  water  is  supplied.  Trees  which  are  suffering  from  dryness,  and 
from  no  other  cause,  show  a  most  marvelous  sending  forth  of  new  shoots 
and  rapidity  of  growth  when  water  is  applied  to  the  roots.  Inversely, 
the  trees  are  as  quick  to  suffer  from  a  lack  of  moisture  as  to  respond  to 
an  addition  of  it.  Their  tendency  is  to  form  a  large  amount  of  new, 
succulent  tender  growth,  both  in  the  top  and  root,  when  water  is  sup- 
plied and  the  distress  of  the  tree  is  proportionately  greater  if  a  shortage 
of  water  follows,  on  account  of  the  presence  of  this  growth. 

Again,  the  tree  is  peculiar  in  being  ready  to  grow  at  any  time  of  year, 
particularly  if  its  growth  has  been  checked  somewhat  by  lack  of  moisture. 
It  has  almost  no  reaction  to  seasonal  conditions.  Normally,  however, 
the  tree  has  three  or  four  fairly  well-defined  periods  of  growth  during 
the  year,  being  intermediate  in  habit  between  deciduous  trees,  which 
have  one  growing  and  one  resting  period,  and  most  evergreen  tropical 
trees  which  grow  more  or  less  continuously  all  the  time. 

Still  further,  a  feature  of  great  importance  is  the  tendency  of  the 
citrus  tree  when  injured  in  any  way,  either  mechanically  or  physiologic- 
ally, to  produce  a  quantity  of  gummy  substance  which  may  run  out  at 
the  wounds  or  break  out  through  the  bark.  The  formation  and  presence 
of  such  gum,  when  once  started,  may  become  a  chronic  source  of  irrita- 
tion to  the  tissues  after  the  cause  of  the  original  injury  has  entirely  dis- 
appeared, and  furthermore,  the  gum  is  often  a  source  of  trouble  through 
the  secondary  fermentation  or  decay  which  it  may  undergo  in  the  tissues 
of  the  plant. 

It  is  the  tendency  in  most  citrus  species,  and  particularly  in  the 
varieties  most  commonly  cultivated,  to  produce  fruit  asexually,  ap- 
parently by  purely  vegetative  growth  without  the  process  of  pollination. 
In  the  Washington  navel  orange,  for  instance,  and  probably  to  a  greater 
or  less  extent  in  other  citrus  fruits  which  are  seedless  or  nearly  so,  the 
fruit  appears  to  be  simply  a  vegetative  growth  like  the  leaves,  rather 
than  a  product  of  sexual  fertilization.  If  this  be  true,  it  is  evident  that 
herein  exists  a  most  important  difference,  from  a  practical  as  well  as 
investigational  standpoint,  between  the  citrus  and  most  other  cultivated 
fruits. 

All  these  peculiarities  are  of  great  significance  in  any  investigation 


Bulletin  218] 


CALIFORNIA   PLANT   DISEASES. 


1135 


concerning  the  citrus  tree,  and  make,  in  California  at  least,  the  con- 
sideration of  plant  physiology,  soil  and  climatic  conditions,  and  other 
similar  factors  of  more  importance  than  the  study  of  parasitic  attacks. 

Gummosis.     See   Lemon.     Figure   49. 
Scaly  Bark.     Figure  63. 

Characterized  by  the  appearance  of  scaly  areas  of  bark  on  the  trunk 
or  branches,  the  outer  bark  rising  in  scales  from  the  inner.     Small  drops 


Fig.  63. — Scaly  bark  of  orange. 

of  gum  exude  in  spots  on  the  affected  portion,  which  gradually  spreads. 
Affected  limbs  die  back  slowly  but  new  growth  keeps  taking  their  place 
and  the  tree  lives  for  many  years  in  an  unhealthy  condition. 

This  trouble  apparently  originates  in  an  irregular  moisture  condition 
of  the  soil.     Practically  all  the  affected  trees  in  the  State  have  been  in 


1136  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION. 

their  present  condition  for  many  years  and  seem  to  have  become  affected 
at  a  time  when  irrigation  by  flooding  was  generally  practiced  and  culti- 
vation received  little  attention. 

The  worst  affected  trees  can  not  be  saved,  but  should  be  dug  out  and 
replaced.  Trees  where  the  disease  exists  only  on  the  branches  will 
recover  if  affected  parts  are  cut  off.  In  case  the  scaly  bark  is  on  the 
trunk  and  the  patch  is  not  too  large  the  diseased  portion  should  be  cut 
out  to  healthy  bark  and  the  wound  painted  over.  Such  cases  will  almost 
invariably  heal  completely. 

If  the  trunk  is  badly  affected,  but  the  tree  in  fairly  good  condition, 
the  scaly  surface  bark  should  be  scraped  off  and  several  slits  cut  through 
the  affected  area.  The  scaly  part  may  then  be  painted  over  with  pure 
neatsfoot  oil,  linseed  oil,  10  per  cent  caustic  soda  or  potash  solution,  or 
kerosene  oil.* 

The  soil  about  the  tree  should  be  thoroughly  dug  up  and  the  applica- 
tion of  oil  or  whatever  is  used  repeated  about  once  a  month  for  several 
months.  This  disease,  as  well  as  the  last,  is  not  contagious  and  no  infec- 
tion need  be  feared  to  neighboring  trees. 

See  Bulletin  200,  California  Experiment  Station. 

Mal  di  gomma. 

A  virulent  decay  of  the  bark  of  the  roots  from  the  surface  of  the 
ground  downward.  This  is  occasionally  found  on  trees  in  extremely 
heavy,  wet  soil  or  where  too  much  water  is  used  close  about  the  trunk 
of  the  tree. 

Affected  trees  can  rarely  be  saved  but  may  be  replaced  successfully  if 
soil  conditions  can  be  improved. 

See  Bulletin  200,  California  Experiment  Station. 

Exanthema — Florida  Die-Back. 

The  branches  die  back  from  the  ends  and  numerous  axillary  buds 
develop,  forming  bushy  tufts  of  small  twigs  all  through  the  top  of  the 
tree.  Corky  outgrowths  develop  on  the  bark  of  the  twigs  and  gum 
exudes  from  these  places.  In  the  first  stages  of  the  disease  there  develop 
near  the  center  of  the  tree  abnormally  large,  dark  green  leaves,  giving 
the  tree  a  false  appearance  of  unusual  thrift.  The  fruit  takes  on  a  pale 
yellow  color  while  still  small  and  immature  and  has  an  insipid  sweetness 
with  no  development  of  acid  quality.  Dark  brown  spots  or  patches 
appear  on  the  rind  and  from  these  as  centers  the  oranges  crack  and  split. 

This  disease  occurs  in  California  mostly  upon  coarse  or  gravelly  soils 
or  subsoils,  following  the  application  of  stable  manure  or  other  nitrog- 
enous material  in  an  organic  form.  It  is  most  apt  to  occur  when  such 
fertilization  is  practiced  on  trees  which  have  not  previously  been  receiv- 


*  Injury  is  sometimes  caused  by  a  too  abundant  use  of  these  substances,  especially 
on  badly  affected  trees. 


Bulletin  218] 


CALIFORNIA    PLANT   DISEASES. 


1137 


ing  it,  especially  if  they  have  been  suffering  somewhat  from  lack  of  plant 
food  and  water.     The  disease  may  be  likened  to  a  form  of  indigestion. 

On  these  soils  citrus  trees  should  receive  very  careful  irrigation  to  the 
end  that  the  ground  may  be  kept  continuously  moist  and  not  be  allowed 
to  become  alternately  wet  and  dry,  as  is  the  tendency  on  such  porous 
soils.  Fertilization  should  be  uniform  without  the  sudden  application 
of  large  amounts  of  manure  or  organic  fertilizers. 

See  Bulletin  200,  California  Experiment  Station. 

Chlorosis. 
This  term  applies  to  cases  where  the  leaves  become  yellow  and  pale, 
lacking  the  normal  green 
color.  No  definite  dis- 
ease is  indicated  by  these 
symptoms,  more  than 
that  the  trees  are  in  dis- 
tress of  some  sort.  The 
cause  of  the  trouble  is 
usually  to  be  found  in 
some  unfavorable  soil 
condition. 


Mottled  Leaf.  Figure  ('A. 
What  has  been  said  in 
the  last  case  applies  to 
this  also.  Affected  trees 
show  a  yellowing  of  the 
leaves  between  the  veins, 
with  the  green  color 
only  along  the  mid  rib 
and  the  lateral  veins, 
giving  the  leaf  a  mottled 
appearance.  Examina- 
tion shows  that  leaves 
once  green  never  become 
typically  mottled  there- 
after, although  they  may  become  lighter  in  color  or  even  bright  yellow. 
Typical  mottled  leaves  are  found  only  toward  the  ends  of  the  shoots  and 
represent  leaves  in  which  the  green  color  has  never  completely  de- 
veloped, rather  than  those  in  which  the  chlorophyll  has  once  existed 
but  then  disappeared.  Mottled  leaf  is  a  case  of  non-development  or 
slow  development  of  chlorophyll.  Along  with  the  mottling  of  the 
leaves  there  also  occurs,  if  the  trees  are  badly  affected,  a  decided  short- 
age in  the  amount  of  fruit  and  in  typically  bad  cases  the  fruit  present 


Fig.  64. — Mottled  leaf  of  orange. 


1138  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION. 

is  of  very  small  size,  becoming  fully  colored  when  only  an  inch  or  two 
in  diameter.  Considerable  die-back  also  occurs  and  the  foliage  is  thin 
and  weak,  giving  the  tree  a  brushy  look,  with  many  small,  dead  twigs  at 
the  extremities. 

Mottled  leaf  is  by  no  means  to  be  always  regarded  as  a  symptom  of 
disease  or  a  cause  for  alarm.  Frequently  in  the  winter  young,  rapidly- 
growing  trees  show  such  a  condition  in  their  youngest  leaves,  especially 
during  periods  of  long  continued  cold  rain.  This  is  to  be  regarded  as 
simply  a  temporary  set-back  in  the  development  of  the  leaves  and  with 
warm  weather  the  normal  green  color  appears  and  the  leaves  soon  put 
on  their  natural  appearance. 

A  more  serious  condition  of  mottled  leaf  may  result  from  any  one  of 
a  variety  of  causes.  It  does  not  necessarily  indicate  any  specific  disease. 
There  has  been,  however,  in  southern  California,  particularly  during  the 
past  year,  quite  a  widespread  condition  of  this  sort,  which  appears  to  be 
of  the  same  general  nature.  This  condition  has  been  attributed  to  a 
variety  of  causes,  most  of  which  probably  had  nothing  whatever  to  do 
with  the  disease.  One  theory  that  has  been  given  prominence  is  that 
mottled  leaf  is  due  to  the  presence  in  the  soil  of  an  excess  of  magnesium 
over  lime.  Not  long  previously  the  opposite  theory  was  held  in  a  similar 
case  in  the  San  Joaquin  Valley,  namely,  that  mottled  leaf  is  due  to  an 
excess  of  lime  in  the  soil.* 

Examination  of  typical  cases  of  mottled  leaf  all  over  the  affected  dis- 
tricts shows  the  following  facts  to  be  true :  The  trouble  is  less  generally 
abundant  near  the  coast  and  more  abundant  inland.  Oranges  are  more 
affected  than  lemons,  and  Valencia  oranges  more  than  Washington 
Navels.  Oranges  top- worked  on  other  citrus  trees  are  worse  affected 
than  those  which  were  budded  in  the  nursery.  Oranges  top-worked  on 
lemon  trees  are  rather  worse  than  those  top-worked  on  orange  trees. 
(The  worst  combination  in  this  respect  is,  therefore,  Valencia  top- 
worked  on  lemon.)  Trees  are  worse  affected  on  the  south  than  on  the 
north  side.  The  most  heavily  fertilized  groves  are  as  badly  and  prob- 
ably more  affected  than  those  which  have  received  less  fertilization. 
( This  is  particularly  the  case  in  connection  with  the  application  of  stable 
manure.)  Orchards  underlaid  with  gravel,  sand  or  sandy  loam  are 
more  affected  than  those  having  a  subsoil  of  fairly  heavy  loam  containing 
no  sand.  Orchards  underlaid  with  plow-sole,  hardpan,  or  extremely 
heavy,  poorly  drained  soil  are  likely  to  be  affected.  In  orchards  where 
a  certain  area  or  streak  of  mottled  leaf  runs  through  the  orchard  this 
corresponds  to  an  area  where  the  subsoil  is  different  and  usually  where 
it  is  coarser.  Young  buds  top-worked  on  large  trees  often  show  mottled 
leaf  for  several  years,  but  gradually  come  out  of  it  and  attain  a  normal 

*  Circular  No.  27,  California  Experiment  Station. 


Bulletin  218]  CALIFORNIA  PLANT  DISEASES.  1139 

condition  as  the  new  tops  become  larger.  Trees  standing  close  to  cor- 
rals or  manure  piles  where  they  receive  a  constant  supply  of  liquid 
manure  are  likely  to  be  badly  affected  with  mottled  leaf. 

All  these  observations  taken  together  point  to  one  conclusion ;  namely, 
that  the  most  prevalent  and  typical  form  of  mottled  leaf  is  due  to  an 
irregular  supply  of  moisture  and  plant  food.  There  should  be  remem- 
bered in  connection  with  the  unusual  prevalence  of  this  trouble  in  1910 
and  1911  the  following  facts :  The  winter  of  1909-10  was  unusually  cold, 
and  citrus  groves  suffered  much  more  than  usual  from  freezing.  In 
the  winter  of  1910  the  rains  stopped  very  early  and  the  spring  was  a 
very  dry  one.  In  the  fall  of  1910  the  rains  were  late  in  commencing, 
so  that  a  period  of  nearly  a  year  elapsed  with  very  little  rainfall.  Irriga- 
tion was  practiced  more  or  less  thoroughly  during  this  unusually  dry 
spring  and  fall,  as  well  as  during  the  summer,  but  all  observation  goes 
to  show  that  in  most  of  the  citrus  groves  the  subsoil  became  much  drier 
than  usual  during  that  season.  Orchards  underlaid  with  either  a  porous 
or  a  hard,  impenetrable  subsoil  were  most  subject  to  this  condition,  as 
discussed  on  page  1069.  The  result  was  that  in  irrigating  only  the  sur- 
face layers  of  soil  were  saturated,  while  between  irrigations  the  soil  dried 
out  much  more  than  commonly.  This  would  have  the  effect  of  giving 
the  tree  an  irregular  nutrition,  soil  food-materials  being  taken  up  at 
the  time  of  irrigation,  but  being  unavailable  during  periods  of  dryness. 

We  are  led  to  the  conclusion  that  this  is  the  nature  of  the  trouble 
from  the  facts  cited  in  regard  to  the  soils  upon  which  mottled  leaf  is 
most  prevalent,  the  fact  that  the  best  fertilized  groves  were  apparently 
more  affected,  other  things  being  equal,  and  the  fact  that  trees  getting  an 
excess  of  nutriment,  like  those  top-budded  and  those  standing  close  to 
manure  piles,  were  the  most  affected.  The  fact  that  interior  districts 
suffered  more  than  those  near  the  coast  and  that  trees  showed  more  effect 
on  the  south  than  on  the  north  side  indicates  that  where  the  sun  was 
hottest,  drawing  most  upon  the  moisture,  the  trouble  became  more  pro- 
nounced. 

We  do  not  wish  to  be  understood  that  the  whole  question  of  mottled 
leaf  may  be  settled  in  this  manner,  but  simply  wish  to  state  these  sug- 
gestive facts.  The  methods  by  which  conditions  tending  to  produce 
this  condition  may  be  improved  are  alluded  to  on  page  1074. 

Die-Rack. 
This  general  term  denotes  cases  where  the  branches  die  back  from  the 
tips.  It  is  not  a  specific  disease,  but  as  in  the  last  two  cases,  indicates 
that  something  is  wrong  with  the  tree.  The  trouble  usually  lies  under- 
ground, and  most  often  denotes  unfavorable  soil  conditions  or  lack  of 
water. 


1140 


UNIVERSITY   OF    CALIFORNIA EXPERIMENT    STATION. 


Trunk  Rot  (Schizophyllum  commune).     Figure  65. 

The  trunk  or  large  limbs  decay  at  points  where  they  have  been  cut 
off  or  injured,  with  the  production  of  small,  white,  bracket  toad-stools 
upon  the  surface.  Not  parasitic  on  sound  trees.  This  also  affects  apples, 
walnuts  and  other  trees. 

Cover  all  large  cuts  or  wounds  thoroughly  with  grafting  wax. 


Fig.  65. — Schizophyllum  trunk  rot  of  orange. 

Root  Rot. 
Citrus  trees  are  affected  by  the  " toadstool' '  or  oak  fungus  disease 
described  under  "Almond,"  whenever  they  happen  to  be  planted  upon 
foot-hill  land  which  has  formerly  grown  oak  trees.  The  trees  die  with 
a  decay  of  the  roots  and  the  white  felty  growth  of  the  fungus  is  found 
between  the  wood  and  bark.     (See  Almond.) 

Twig  Blight   (Rclcrotinia) .     See  Lemon. 

Wither-Tip,  Anthracnose,  "Tear  Stain." 

The  wither-tip  fungus  described  in  connection  with  the  lemon  has  a 

somewhat  similar  relation  to  the  orange.    The  fungus  occurs  abundantly 

upon  dead  or  injured  twigs,  leaves  or  trees,  but  is  of  doubtful  occurrence 


Bulletin  218] 


CALIFORNIA   PLANT   DISEASES. 


1141 


as  a  true  parasite.  This  fungus  occasionally  causes  a  decay  of  the  fruit 
of  the  orange,  quite  different  from  anything  seen  in  the  lemon.  The 
wither-tip  rot  of  the  orange  consists  in  a  large,  rather  dry,  brown  spot, 
starting  sometimes  on  fruit  while  on  the  tree  during  wet  weather,  and 
gradually  spreading.  These  spots  usually  develop  at  places  where 
oranges  touch  each  other.  The  same  spotting  and  decay  is  quite  fre- 
quently found  to  a  considerable  extent  in  oranges  held  in  cold  storage, 
particularly  if  the  temperature  is  a  little  too  low.  Under  such  condi- 
tions this  fungus  may  develop  abundantly  and  cause  a  considerable 
amount  of  decay. 

Damping  Off   (Rhizoctonia,  Fusarium).     Figure  66. 

Causes  the  loss  of  great  quantities  of  orange  seedlings  in  the  seed 
bed.  The  plants  begin  to  die  in 
spots  which  gradually  extend, 
finally  involving  large  areas  if 
not  checked.  Two  distinct  forms 
of  the  disease  are  recognizable, 
one  caused  by  the  first  named 
fungus  above,  producing  a  decay 
of  the  stem  just  above  ground, 
while  the  other  shows  itself  in 
dead  spots  on  the  stem  at  any 
point. 

These  troubles  can  only  be  con- 
trolled by  strict  attention  to 
proper  methods  of  planting  and 
watering.  The  seed  bed  should 
be  constructed  with  an  inch  of 
clean,  fresh  sand  on  top,  with 
heavier  soil  beneath.  For  the 
inexperienced  grower,  particu- 
larly, it  is  better  to  make  fur- 
rows six  inches  deep  and  about 
a  foot  apart,  planting  the  seed 
broadcast  on  the  ridges  between. 
The  water  may  then  be  run  in 

these     furrOWS     and     allowed     tO       FlG<  66.— Damping  off  of  orange  seedlings. 

soak  into  the  ground  laterally,  rather  than  being  sprinkled  on  the 
surface.  Where  the  seed  is  sown  broadcast  all  over  the  surface  of 
the  bed  and  the  water  applied  by  sprinkling,  watering  should  always 
be  done  in  the  morning  and  no  oftener  than  is  absolutely  neces- 
sary. In  many  cases  a  good  watering  once  a  week  is  sufficient  to  keep 
the  soil  under  the  sand  wet  enough  and  twice  a  week  is  almost  always 
sufficient  until  the  plants  get  quite  large.    It  is  better  to  give  the  bed 


1142 


UNIVERSITY    OF    CALIFORNIA — EXPERIMENT    STATION. 


a  good  soaking  at  long  intervals  rather  than  to  keep  sprinkling  on  a 
little  water  frequently.  One  should  keep  the  surface  as  dry  as  possible 
and  after  the  plants  get  well  started  determine  the  need  of  water  by 
digging  down  into  the  soil  beneath  rather  than  wetting  the  bed  as 
soon  as  the  surface  sand  gets  dry. 

Leaf  Spot — Gum  Spot.     Figure  G7. 
Dark  colored,  slightly  raised  spots  or  areas*  appear  on  the  back  side  of 


Fig.  67. — Gumming  of  orange  leaves. 

the  leaf  in  places  where  it  is  turned  up  and  exposed  to  the  sun.  These 
spots  are  formed  by  the  deposition  of  a  gummy  substance  in  the  tissue. 
The  trouble  appears  to  be  in  a  form  of  gumming  resulting  from  sunburn 
on  the  under  side  of  the  leaf.    Not  serious. 

Blue  Mold   (Penicillium  italicum  and  P.  digitatum).     Figure  54. 
The  fruit  shows  a  soft,  moldy  decay,  the  surface  of  the  affected  portion 
being  covered  with  a  dusty  mass  of  spores,  of  a  blue  or  green  color, 
according  as  the  first  or  second  named  fungus  is  present.     The  blue 


Bulletin  218] 


CALIFORNIA   PLANT   DISEASES. 


1143 


fungus  is  somewhat  more  active  than  the  green  and  causes  occasional 
infection  by  contact  from  one  fruit  to  another. 

The  two  fungi  named  above  are  the  commonest  cause  of  decay  in  citrus 
fruit.  Only  very  slightly  parasitic  on  uninjured  fruit;  this  decay  is 
practically  confined,  under  ordinary  conditions,  to  fruit  which  has  been 
injured  in  handling. 

The  extensive  demonstrations  of  the  United  States  Department  of 
Agriculture  have  established  beyond  question  that  citrus  fruit  will 
keep  indefinitely  so  far  as  blue  mold  decay  is  concerned,  unless  the  fruit 
has  been  bruised  or  injured  in  some  manner.  Such  injury  comes  about 
mainly  either  through  cuts  in  the  stem  end  made  in  clipping  the  fruit 
from  the  tree,  from  rough  handling  during  the  process  of  hauling  to 
the  packing  house,  or  in  grading  or  packing.  As  a  result  of  the  demon- 
stration mentioned  above,  the  whole  practice  of  citrus  fruit  handling 
in  California  has  been  revolutionized  along  the  line  of  more  careful 
handling,  and  implements 
and  apparatus  tending  to- 
ward less  injury  in  pick- 
ing and  handling  fruit 
have  been  developed.  Each 
year 's  experience  goes  more 
and  more  to  demonstrate 
the  possibilities  of  almost 
absolute  prevention  of  this 
commonest  form  of  decay 
through  careful  handling. 


Navel  Rot — Black   Rot. 
(Altemaria  citri) .     Figure  68. 

Affected  oranges  color 
prematurely  in  the  fall  and 
are  affected  with  a  dry, 
black  rot  in  the  tissue  below 


Fig.  68. — Navel  rot  of  orange  (Altemaria  citri), 


the  navel  end.  This  rot  is  not  very  virulent  and  often  remains  con- 
fined to  one  section  of  the  orange.  Occasionally  in  seasons  of  consider- 
able early  rain  this  trouble  becomes  quite  abundant,  but  it  is  not 
usually  a  serious  matter. 

Brown  Rot.  See  Lemon. 
Brown  Spot.  Figure  69. 
A  serious  trouble  in  some  localities,  characterized  by  the  development 
of  dark  brown,  sunken,  dead  spots  of  considerable  size  on  the  rind,  ap- 
pearing from  five  to  ten  days  after  the  fruit  is  picked.  Not  visible  on 
the  tree.  Apparently  due  to  climatic  or  other  local  conditions  rather 
than  to  any  parasite. 


1144  UNIVERSITY   OF    CALIFORNIA — EXPERIMENT   STATION. 

The  nature  of  brown  spot  appears  to  be  that  of  a  premature  dying  of 
the  rind  in  certain  spots.  The  fruit  shows  absolutely  no  indication  of 
any  such  trouble  while  it  is  on  the  tree  or  immediately  after  picking, 
but  after  a  few  days  have  elapsed  these  sunken,  dark  colored,  dead 
spots  begin  to  appear.  Some  years  they  become  darker  in  color  than 
others.  So  far  as  known  the  trouble  only  affects  the  Washington  navel 
orange  and  is  worst  on  the  smoothest,  highest  quality  fruit.  Coarse, 
rough  fruit  is  not  as  likely  to  be  affected.  The  trouble  is  usually  much 
more  prevalent  in  the  inland  districts  with  hotter  weather  in  summer, 
than  it  is  out  toward  the  coast.  The  earliest  picked  fruit  is  much  more 
affected  than  that  left  on  the  trees  until  late  in  the  season  and,  in  fact, 
brown  spot  usually  disappears  almost  entirely  after  January.  For  this 
reason  the  growers  have  a  theory  that  the  occurrence  of  heavy  winter 
rains  stops  this  trouble.     Fruit  picked  very  early,  while  still  green, 


Fir.  69. — Brown  spot  of  orange. 

say  early  in  October,  shows  the  spot  very  decidedly,  the  spots  remaining 
green  when  the  rest  of  the  rind  has  turned  to  its  normal  yellow  color. 
Fruit  from  all  sides  of  the  tree  appears  to  be  equally  affected,  so  far  as 
has  been  determined.  Various  forms  of  spotting  may  be  found  on  navel 
oranges  while  still  on  the  tree,  but  it  is  certain  that  brown  spot  has  no 
connection  with  any  of  these,  but  that  the  true  brown  spots  develop  in 
portions  of  the  rind  which  are  absolutely  smooth  and  unblemished  when 
the  fruit  is  picked. 

It  would  appear  that  in  the  physiological  processes  which  go  on  in  the 
rind  during  its  development  and  ripening,  some  substance  or  principle 
is  present  in  certain  areas  which  inhibits  these  normal  processes.  When 
the  orange  is  picked  early  in  the  season  it  appears  that  this  inhibiting 
substance  is  in  an  active  condition  and  causes  the  area  of  tissue  where  it 
is  present  to  begin  to  die  as  soon  as  the  fruit  leaves  the  tree.  If  the 
orange  stays  on  the  tree  until  later  in  the  season  the  injurious  substance 


Bulletin  218] 


CALIFORNIA   PLANT   DISEASES. 


1145 


seems  to  disappear  or  be  removed  in  some  manner,  leaving  the  rind  in 
a  normal  condition.  When  decolorized  and  treated  with  iodine,  the  rind 
of  oranges  freshly  picked  in  a  brown  spot  season  and  locality  shows  the 
presence  of  an  accumulation  of  starch  in  areas  here  and  there,  corre- 
sponding to  about  the  size  and  distribution  of  the  brown  spots  which 
would  have  developed  on  the  same  oranges  if  they  had  been  kept  for  a 
week  or  two.  If  tested  in  the  same  way  after  the  spots  have  developed, 
an  accumulation  of  starch  is  similarly  found  in  the  areas  forming  the 
spots.  It  therefore  appears  that  diastatic  action  in  these  areas  is  in- 
hibited in  some  way. 

Investigation  has  thus  far  failed  to  demonstrate  the  nature  of  the 


Fig.  70. — Puffing  of  orange  fruit. 

initial  injury,  whether  due  to  some  climatic  condition,  lack  of  moisture, 
or  possibly  an  insect  puncture.  It  is  certainly  not  due  to  frost  or  cold 
weather.  The  fruit  from  certain  groves  seems  to  show  the  trouble  more 
than  that  from  others,  and  it  is  possible  that  the  same  is  true  of  individ- 
ual trees,  but  this  has  not  yet  been  determined. 

See  Bulletin  203,  page  47,  California  Experiment  Station. 

Splitting. 
The  fruit  cracks  and  splits  on  the  tree  before  maturity.    Varies  from 
year  to  year  in  abundance.    Apparently  caused  by  climatic  or  seasonal 
conditions  causing  irregularity  in  the  growth  of  the  fruit. 


1146  UNIVERSITY    OF    CALIFORNIA — EXPERIMENT    STATION. 

Puffing.     Figure  70. 

Characterized  by  a  condition  of  the  rind  indicated  by  the  above  name. 
The  surface  of  the  fruit  becomes  rough  and  uneven,  due  to  a  spongy 
condition  of  the  rind.  The  whole  orange  becomes  soft  and  structureless 
with  an  unnatural  sweetness. 

This  trouble  varies  with  the  season  and  appears  to  be  connected  with 

soil  moisture  conditions. 

Stain. 

A  discolored,  darkened  condition  of  the  rind  developing  after  the 

fruit  has  been  picked.     Occurrence  apparently  confined  to  fruit  which 

has  been  subjected  to  low  temperatures,  either  in  transit  or  cold  storage. 

Shoulder  Spot — Stem  End  Spot.  Figure  71. 
A  dry,  brown,  dead  spot  or  area  develops  upon  the  orange  about  the 
stem  end  or  at  one  side  of  the  latter  on  the  "shoulder''  of  the  fruit. 
These  spots  are  primarily  dry  and  not  of  the  nature  of  decay,  but  they 
often  become  infected  with  blue  mold  or  other  fungi.  Often,  too,  they 
are  covered  with  a  growth  of  a  Cladosporium  fungus,  which  forms  an 
almost  black  mold  upon  the  surface.  These  spots  may  also  become  in- 
fected with  the  wither-tip  fungus.  This  form  of  spot  or  deterioration 
at  the  stem  end  of  the  orange  occurs  only  in  old  fruit,  most  commonly  in 
the  last  Washington  Navels  of  the  season.  It  is  especially  abundant  in 
seasons  following  years  of  exceptional  drouth,  particularly  when  the 
fall  rains  are  very  late  in  commencing.  The  normal  deterioration  of  the 
orange  when  its  physiological  life  is  ended  begins  at  the  stem  end  and 
the  present  trouble  appears  to  be  simply  a  somewhat  premature  death 
of  the  tissue,  owing  to  the  age  and  weakness  of  the  fruit.  This  is  made 
more  pronounced,  as  has  just  been  suggested,  by  a  long,  dry  season 
during  the  preceding  fall  which  weakens  the  tree  and  thus  reduces  the 
vitality  and  length  of  life  of  the  fruit. 

Miscellaneous  Spots  and  Blemishes. 
Oranges  and  other  citrus  fruits  are  subject  to  a  variety  of  surface 
spots  and  blemishes.  In  a  paper  prepared  by  Dr.  J.  Eliot  Coit  of 
this  Department,  published  in  the  California  Cultivator  of  March  16, 
1911,  about  fifty  different  forms  of  such  blemishes  are  classified  and 
described.  These  are  classified  as  being  caused  by  insects,  fungi,  me- 
chanical injuries  and  physiological  troubles.  Those  which  we  have 
described  above  are  by  far  of  the  most  importance,  although  occasionally 
in  certain  seasons  some  other  form  of  spotting,  blemish  or  injury 
occurs  which  attracts  considerable  attention  for  a  temporary  period. 
Frequently  in  such  cases  certain  mold  fungi  develop  upon  the  surface 
of  the  areas  affected  and  are  sometimes  taken  for  the  cause  of  the  trouble. 
This  is  particularly  the  case  with  a  species  of  Cladosporium  which  pro- 


Bulletin  218] 


CALIFORNIA    PLANT    DISEASES. 


1147 


Fig.  71. — Shoulder  spot  of  orange. 


1148 


UNIVERSITY   OF    CALIFORNIA — EXPERIMENT   STATION. 


duces  a  dark  brown  mold  on  the  surface  of  the  spots.  This  fungus,  how- 
ever, has  nothing  to  do  with  originating  any  form  of  spot  upon  citrus 
fruit. 

Palm    (Phoenix  canariensis,  dactylifera,   etc.). 
Leaf  Spot  (Graphiola  phoenicis).     Figure  72. 

Injures  the  lower  leaves  of  the  date  palms  with  the  production  of 
minute  black  protuberances  of  the  fungus,  mostly  on  the  lower  side  of 
the  leaves. 

Remove  all  affected  leaves,  and  if  this  fails  to  control  the  trouble  the 


Fig.   72. — Palm  leaf  spot   (Graphiola  phoenicis). 


Fig.     73. — Palm    leaf     spot     (Sphaerodothis 
neowashingtoniae) . 


trees  may  be  sprayed  with  the  ammoniacal  copper  carbonate.    Bordeaux 
mixture  is  effective,  but  disfigures  the  tree. 

Palm  (Washingtonia) . 
Leaf  Spot   (Sphaerodithis  neowashingtoniae) .     Figure  73. 

The  leaves  become  covered  with  small,  elongated,  black,  slightly  ele- 
vated spots  of  the  fungus  growth,  and  die.' 
Affected  leaves  should  be  removed. 


Bulletin  218] 


CALIFORNIA   PLANT   DISEASES. 


1149 


PEA. 
Mildew  (Erysiplie  polygoni). 
Covers  the  plants  and  pods  with  a  white  mildew.    Most  prevalent  in 
wet  weather  and  is  usually  only  serious  on  the  winter  crop. 

Dust  the  vines  with  dry  sulphur  at  the  first  appearance  of  the  trouble. 
In  cloudy  weather  spraying  with  Bordeaux  mixture  is  most  effective. 

Blight  (Ascochyta  pisi). 
Produces  black  spots  on  the  leaves  and  pods  and  seriously  injures  the 
vine.    Most  troublesome  in  wet  weather. 


i  0   _,  1 


Fig.    74. — Curl    leaf    of   peach    (Exoascus    defor- 
mans). 

Spray  with  Bordeaux  mixture  if  the  trouble  is  serious 
enough  to  make  it  profitable. 

PEACH. 

Leaf  Curl   {Exoascus  deformans) .     Figure  74. 

Many  of  the  leaves  are  curled  and  deformed  in  a  char- 
acteristic manner  as  they  develop  in  the  spring.  These 
afterward  wither  and  fall,  together  with  much  of  the 
fruit.  A  new  crop  of  leaves  then  develops  in  a  normal 
manner. 

Spray  with  Bordeaux  mixture  or  lime-sulphur  just    fig.  75. Peach 

before  the  buds  open  in  spring.  blight  (Coryneum 

r  xr        a  beyennkii). 

Blight  (Coryneum  oeyerinkii).     Figure  75. 
Dead  spots  appear  on  the  young  shoots  during  the  winter,  particularly 
at  the  buds.     The  buds  are  killed,  together  with  much  of  the  young 
8— Bul.  218 


1150 


UNIVERSITY   OF    CALIFORNIA — EXPERIMENT   STATION. 


growth  or  fruiting  wood.  During  the  spring  rains  a  jelly-like  gum 
exudes  in  large  quantities  from  these  dead  spots. 

Spray  with  Bordeaux  mixture  during  November  and  again  with  the 
same  material  or  lime-sulphur  just  before  the  buds  open.  A  combined 
spraying  may  be  made  for  blight,  curl  leaf  and  peach  worm  by  using 
Bordeaux  in  the  fall  and  lime-sulphur  in  the  spring. 

See  Bulletin  191,  California  Experiment  Station. 

Mildew   (Podosphaera  oxyacanthce) . 

A  white  powdery  mildew  appearing  on  the  leaves  during  the  summer. 

Not  serious. 

Die-Back.     See  Almond. 


Fig.  76. — Little  peach. 

Little  Peach.     Figure  76. 
Some  or  all  of  the  peaches  remain  small  and  undeveloped,  while  the 
normal  fruit  is  reaching  full  size. 

This  is  not  the  dreaded  little  peach  disease  of  eastern  states,  but 
appears  to  be  the  effect  of  imperfect  pollination.  Its  occurrence  has 
been  found  to  follow  seasons  of  much  rainfall  during  the  blossoming 
period.  Not  serious.  In  some  cases  Fruit  Drop  occurs  from  the  same 
cause.    See  Almond. 

Brown  Rot.     See  Apricot. 

Cbown  Gall,  Root  Rot,  Sour  Sap,  Rust.     See  Almond. 

Gummosis.     See  Cherry. 


Bulletin  218]  CALIFORNIA  PLANT  DISEASES.  1151 

Split  Pit. 
The  pit  cracks  and  splits  into  many  small  fragments  while  the  fruit 
is  still  on  the  tree.    Cause  not  known,  but  apparently  climatic.    Possibly 
due  to  frost  injury  in  spring. 

Fruit  Gumming. 
Masses  of  gum  appear  on  the  surface  of  the  fruit,  which  may  be  traced 
through  the  flesh  to  their  origin  in  the  pit.    Apparently  somewhat  con- 
nected with  the  last  trouble. 

Little  Leaf — California  Yellows.     Figure  77. 

Characterized  by  the  development  of  spindling,  yellow,  sickly  looking 
shoots  on  the  new  growth,  with  small,  narrow,  yellow  leaves.  The  leaves 
along  the  shoots  drop  off  during  the  summer,  leaving  tufts  at  the  ends. 
Fruit  fails  to  develop,  shrivels  and  drops.  Worst  on  trees  from  three  to 
seven  years  old. 

This  trouble  also  attacks  other  stone  fruits,  walnuts,  pecans  and  other 
trees.  Always  worst  on  lighter,  drier  soils,  this  feature  showing  itself 
by  the  more  pronounced  occurrence  of  the  disease  on  trees  standing  in 
sandy  streaks  or  slight  elevations  in  the  orchard. 

This  trouble  has  no  relation  to  the  true  Eastern  peach  yellows,  but  is 
decidedly  climatic  and  seasonal  in  its  appearance.  Occurs  mostly  follow- 
ing unusually  dry  seasons,  on  trees  standing  in  light  soil  or  one  under- 
laid with  a  coarse,  sandy  subsoil.  Trees  on  a  fairly  heavy  subsoil,  or 
those  which  have  received  abundant  irrigation  throughout  the  preced- 
ing season  are  decidedly  free  from  the  trouble  even  in  the  worst  affected 
localities.  Appears  similar  in  nature  to  " mottled  leaf"  of  the  orange, 
and,  in  fact,  orange  trees  growing  near  peaches  affected  by  ' '  little  leaf ' 
show  a  typical  "mottled  leaf"  condition.  Many  other  kinds  of  trees  are 
also  more  or  less  affected. 

The  typical  peach  disease  has  been  seen  only  in  the  San  Joaquin 
Valley,  in  the  most  sandy  regions. 

In  most  cases,  regular  irrigation  during  the  summer  shows  a  marked 
effect  in  controlling  this  trouble.  Such  irrigation  should  be  given  partic- 
ularly in  the  latter  part  of  the  season,  after  the  crop  is  off,  especially 
when  the  rains  are  late  in  commencing. 

Climatic  Effect. 
The  trees  fail  to  leaf  out  properly  in  the  spring  and  seem  to  become 
confused,  so  to  speak,  as  to  the  season.  Later  in  the  summer  the  trees 
may  bloom  and  leaves  begin  to  appear,  but  the  tops  usually  die  back 
nearly  to  the  forks  of  the  tree  and  sometimes  the  trees  die  entirely.  If 
not  too  badly  affected,  the  tree  sends  out  new  sucker  growth  from  the 
trunk  and  base  of  the  main  limbs.  Plums,  apricots,  apples  and  other 
trees  are  sometimes  affected. 


1152 


UNIVERSITY   OF    CALIFORNIA — EXPERIMENT   STATION. 


This  trouble  is  one  which  occurs  mostly  in  the  southern  part  of  the 
state  as  a  result  of  unseasonable  climatic  conditions.  It  is  usually  most 
pronounced  in  seasons  when  a  period  of  warm,  stimulating  rains  in  the 
winter  is  followed  by  a  long,  cold  spring.    Similar  results  are  also  pro- 


Fig.  77. — Little  leaf  of  peach. 

duced  by  an  abnormal,  dry  fall,  throwing  the  trees  into  a  dormant  con- 
dition, followed  by  warm,  spring-like  weather  accompanying  the  winter 
rains.  These  combinations  and  various  others  often  have  unfavorable 
effects  upon  trees  which  are  accustomed  to  a  definite  resting  period  dur- 
ing the  winter.     Many  peculiar  diseases  of  deciduous  fruits  described 


Bulletin  218] 


CALIFORNIA   PLANT   DISEASES. 


1153 


in  this  bulletin  under  various  names,  such  as  "die-back,"  "yellows/ 
etc.,  are  no  doubt  contributed  to  by  such  disturbances  in  the  normal 
period  of  dormancy.     Every  few  years  there  is  usually  a  season,  espe- 
cially in  the  southern  part  of  the  State,  when  deciduous  trees  are  badly 
affected  in  such  ways  as  these. 

Following  such  an  attack,  trees  should  be  pruned  back  to  healthy, 
vigorous  wood,  when  they  will  usually  form  a  new  top  and  come  back 
into  good  condition  again.  With  peaches  it  is  noticeable  that  varieties 
of  the  saucer  or  Peen  To  type  are  not  affected  in  this  manner,  as  are 
the  Persian  varieties. 

PEAR. 
Scab   (Venturia  pirina).     Figure  78. 

Similar  to  apple  scab,  which  see.  Develops  as  a  dark  brown  fungus 
in  spots  on  the  young  pear  or  even  in  the  blossoms.    Also  on  the  under 


Fig.  78. — Pear  scab  (Venturia  pirina). 

side  of  the  leaves.  Much  worse  in  sections  with  abundant  moisture  in 
spring.  Often  causes  much  of  the  fruit  to  fall  at  the  very  first  of  its 
development,  while  the  affected  pears  which  remain  on  the  tree  are 
scabby  and  much  deformed. 


1154 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION. 


Spray  with  Bordeaux  mixture.  See  Apple  Scab.  Combined  spraying 
may  be  done  for  scab  and  codling  worm. 

See  Bulletin  163,  California  Experiment  Station. 

Blight  (Bacillus  amylovorus).  Figure  79. 
The  leaves,  blossoms  and  young  fruit  wither  and  turn  black  on  the 
affected  portions  but  do  not  fall,  remaining  tightly  attached  to  the 
twigs  during  the  winter  after  the  green  leaves  have  fallen.  Caused  by 
a  bacterial  organism  which  produces  its  infection  largely  through  the 
blossoms,  being  carried  by  insects  from  tree  to  tree.  The  infection  pro- 
ceeds downwards  through  the  inner  bark  of  the  twigs  and  branches  and 
when  working  vigorously  the  blight  kills  the  twigs  or  whole  branches 

very  rapidly.  The  dis- 
ease often  runs  down  into 
the  large  limbs,  where  it 
remains  alive  over  winter, 
producing  the  so-called 
' '  hold-over ' '  blight,  which 
is  a  source  of  infection 
during  the  following  sea- 
son. 

The  blighted  twigs, 
branches  or  trunks  show 
a  red,  sappy,  juicy  condi- 
tion of  the  inner  bark 
when  infected  with  the 
true  pear  blight  organism. 
If  the  disease  is  fresh  and 
active  the  bark  when  cut 
into  is  very  juicy,  exuding 
the  slightly  sticky  sap 
quite  freely  and  showing 
the  characteristic  bright 
red  color  in  the  inner 
bark.  This  symptom  is  of 
importance  in  distinguishing  true  blight  from  such  troubles  as  sour  sap, 
crater  blight  and  black  leaf. 

In  the  smaller  twigs  and  branches  the  organism  dries  out  and  becomes 
entirely  dead.  Infection  also  takes  place  through  the  agency  of  biting 
insects  in  the  young  shoots  and  suckers.  Through  this  means  the  dis- 
ease frequently  gets  into  the  trunk  of  the  tree  and  also  down  into  the 
roots.  Here  it  spreads  and  causes  the  death  of  the  tree  by  slow  de- 
grees, due  to  the  destruction  of  the  inner  bark  of  the  trunk  or  main 
roots.     In  such  cases  the  leaves  of  affected  trees  take  on  a  peculiar 


Fig.  79. — Pear  blight   (Bacillus  amylovorus) 


Bulletin  218]  CALIFORNIA  PLANT  DISEASES.  1155 

bronzy  reddish  coloration  in  the  fall,  which  is  quite  characteristic  to 
the  experienced  eye. 

From  the  "hold-over"  blight  in  the  trunks  and  large  limbs  an  in- 
fectious sap  exudes  when  growth  starts  in  the  spring,  which  sap  con- 
tains myriads  of  the  blight  organism.  This  sap  is  attractive  to  insects, 
which,  in  feeding  upon  it,  get  the  blight  bacteria  upon  their  bodies  and 
mouth  parts;  and  transfer  them  to  the  blossoms  or  green  shoots  of  other 
trees,  thus  spreading  the  infection. 

Cut  out  and  destroy  all  diseased  parts,  taking  care  particularly  in 
the  summer  time  to  cut  far  below  any  visible  sign  of  the  disease,  even 
at  the  sacrifice  of  considerable  fruit.  The  pruning  instruments  should 
be  kept  constantly  disinfected,  using  a  solution  of  corrosive  sublimate 
(bichloride  of  mercury)  1-1000. 

Trees  badly  affected  in  the  trunk  or  roots  should  be  taken  out  and 
destroyed,  unless  it  is  possible  to  cut  out  all  the  affected  tissue  of  the 
inner  bark,  which  can  be  identified  by  its  reddish  color.  In  some  cases 
the  affected  tissue  can  thus  be  removed,  cutting  back  to  sound  bark  and 
wood  on  all  sides,  and  the  tree  saved.  In  doing  this  work  the  tools 
should  be  thoroughly  disinfected,  and  the  wounds  saturated  with  the 
disinfectant  and  afterwards  painted  over  with  white  lead  paint. 

See  Bulletin  184,  page  221,  and  Bulletin  203,  page  18,  California 

Experiment  Station. 

Black  Leaf. 

In  this  disease  one  side  or  one  limb  of  the  pear  tree  dies  and  the 
leaves  turn  black  and  hang  on  for  some  time.  The  effect  is  quite  similar 
in  a  general  way  to  that  of  pear  blight,  but  there  is  no  sign  of  the 
presence  of  the  pear-blight-causing  organism  as  indicated  by  the  red, 
juicy  inner  bark  of  limbs  and  twigs  affected  with  the  real  blight.  Some- 
times there  is  connected  with  black  leaf  a  dying  of  the  bark  extending 
in  a  narrow  strip  of  uniform  width  down  the  trunk  to  the  ground.  All 
phases  of  this  disease  are  distinguished  from  the  true  blight  by  the 
fact  mentioned  that  there  is  not  present  the  red,  juicy  condition  of  the 
inner  bark,  but  the  bark  simply  dies  down  and  becomes  very  hard  and 
dry  from  the  first.  This  trouble  also  often  occurs  in  orchards  where 
the  blight  is  not  present  and  does  not  show  the  characteristic  spreading 
of  blight  from  tree  to  tree  through  the  blossoms  or  by  infection  of 
young  shoots  and  suckers. 

The  disease  appears  to  be  more  of  the  nature  of  sour  sap,  connected 
most  commonly  with  an  excessive  amount  of  moisture  in  the  ground 
during  the  winter  and  spring.  Where  individual  limbs  are  affected  or 
narrow  strips  of  bark  on  the  side  of  the  trunk,  it  appears  that  certain 
roots  have  been  badly  injured  and  that  the  portions  affected  above 
ground  correspond  with  such  roots. 


1156  UNIVERSITY   OF    CALIFORNIA EXPERIMENT    STATION. 

Crater  Blight. 
This  term  is  a  rather  common  one  among  pear  growers,  but  is  not 
applied  to  any  very  definite  form  of  disease.  It  is  supposed  to  signify 
a  dying  of  certain  spots  or  patches  of  bark  situated  on  the  limbs  or 
trunk.  In  these  patches  the  bark  becomes  rough  on  the  outside  and  dark 
colored  beneath  the  surface.  Some  injury  of  this  sort  appears  to  be 
connected  with  the  disease  described  above,  the  bark  dying  in  certain 
spots  rather  than  in  a  strip  up  and  down  the  whole  length  of  the  branch 
or  trunk.  True  pear  blight  may  also  cause  a  similar  effect  by  running  in 
from  a  small  shoot  or  fruit  spur,  but  many  cases  of  both  black  leaf  and 
crater  blight  occur  without  the  presence  of  the  pear  blight  organism. 
Frequently,  what  is  called  crater  blight  is  renlij  nothing  more  than  the 
normal  roughening  of  the  bark  of  the  pear  tree  as  it  grows  older.  In 
this  tree  the  bark  begins  to  crack  and  roughen  in  patches  on  the  trunk 
and  main  limbs,  and  its  normal  condition  has  sometimes  the  appearance 
of  the  outbreak  of  some  disease. 

Cukly  Bark. 
This  is  somewhat  similar  to  the  above,  the  bark  cracking  in  concentric 
rings  in  spots  upon  the  surface  of  the  main  limbs.    It  is  not  of  any  seri- 
ous consequence. 

Fruit  Drop. 

The  young  fruit  drops  from  the  tree  while  still  very  small  and  im- 
mature. Due  to  imperfect  pollination.  Ordinarily,  results  simply  in 
a  desirable  thinning  of  the  fruit,  but  sometimes  a  large  part  of  the 
crop  drops  from  this  cause.  May  also  be  produced  by  frost  affecting  the 
fruit  soon  after  setting.  Such  fruit  may  remain  on  the  tree  and  con- 
tinue to  grow  for  some  time  after  the  frost  occurs  before  falling. 

Ringed  Fruit. 
Some  years  many  pears  are  found  at  maturity  with  a  scabby  ring  or 
belt  of  considerable  width  extending  around  the  fruit.  The  pears  are 
constricted  in  this  portion,  owing  to  interference  with  the  growth.  It 
is  evident  that  this  effect  comes  about  through  some  injury  to  the  pear 
when  it  is  quite  young.  This  is  a  frost  effect,  and  pears  in  a  very  small, 
young  condition  may  be  seen  with  similar  rings  about  them  in  a  season 
when  much  damage  has  been  caused  by  late  frost. 

PECAN. 

Rosette  or  Frizzies. 

While  not  an  important  crop  in  California,  there  is  considerable  inter- 
est at  present  in  pecan  planting,  and  it  is  desirable  to  call  attention  to 
this  disease. 

Shoots  develop  of  a  spindling,  yellow,  frizzly  appearance,  continually 


Bulletin  218]  CALIFORNIA  PLANT  DISEASES.  1157 

dying  back  and  shooting  out  anew  from  axillary  buds.  The  trouble 
is  very  similar,  if  not  identical,  with  that  affecting  the  walnut  and  also 
seems  to  be  related  to  what  we  have  described  as  the  California  peach 
yellows.  It  is  probably  the  same  as  the  pecan  rosette,  which  occurs  in 
the  southeastern  states. 

PLUM. 

Die-Back,  Crown  Gall,  Sour  Sap,  Rust.     See  Almond. 

Brown  Rot.     See  Apricot 

POMELO.     See  Orange. 

POTATO. 

Scab  (Oospora  scabies).     Figure  80. 
The  growth  of  this  fungus  on  the  surface  of  the  potato  produces  a 
rough,  scabby  condition  greatly  injuring  its  appearance  and  selling 


Fig.  80. — Potato  scab  (Oospora  scabies). 

value.     Possibly  this  or  a  similar  condition  is  also  caused  by  other 

agencies  than  the  fungus  above  named. 

Use  clean  seed,  treating  before  planting  or  cutting  by  soaking  one  and 

one  half  hours  in  a  solution  of  one  pint  of  formalin  to  thirty  gallons  of 

water.    If  the  soil  is  badly  infested,  do  not  use  it  for  potatoes  for  several 

years. 

Early  Blight  (Alternaria  solani). 

Produces  dead  spots  on  leaves.    Not  serious  in  this  State. 
Late  Blight   (Phytophthora  infestans) . 

Causes  death  of  the  leaves  and  decay  of  the  tubers.  This  fungus  de- 
velops only  when  considerable  moisture  is  present  in  the  air,  and  its 
attacks  on  potatoes  in  California  are  therefore  confined  to  those  grown 
in  the  winter  season  or  in  very  foggy  localities  near  the  coast.    Under 


1158  UNIVERSITY   OF    CALIFORNIA — EXPERIMENT   STATION. 

either  of  these  conditions  the  disease  may  develop  very  disastrously  and 
suddenly,  killing  down  and  blackening  the  potato  tops,  as  though  they 
were  struck  by  frost. 

Spray  with  Bordeaux  mixture  immediately  after  rains  or  during 
foggy  weather,  if  treatment  seems  necessary. 

Dry  Rot  (Fusarium  oxijsporum) . 

This  fungus  causes  a  decay  of  the  stems  and  main  roots,  resulting  in 
a  gradual  wilting  and  dying  of  the  plants.  Affected  potatoes  show  a 
dark  ring  just  inside  the  surface  and  from  this  the  fungus  may  spread 
all  through  the  tuber,  producing  a  dry  rot.  Potatoes  in  storage  some- 
times develop  this  quite  extensively.  The  parasite  is  thus  carried  in 
the  seed  and  can  be  controlled  only  by  planting  potatoes  which  are 
free  from  this  fungus. 

Use  seed  known  to  be  from  a  crop  not  affected  by  this  trouble  and 
do  not  plant  potatoes  in  badly  infested  soil. 

Brown  Streak. 
The  tubers  show  a  brown  ring  or  streaks  in  the  flesh  just  beneath  the 
surface,  and  sometimes  throughout.  This  is  sometimes  confused  with 
the  disease  preceding,  but  there  appears  to  be  a  distinct  trouble  of  this 
sort  in  which  no  fungus  can  be  found.  Occurs  particularly  in  foothill 
and  mountain  districts.  Apparently  clean  seed  from  outside  districts 
develops  the  trouble  in  the  first  crop  in  affected  regions. 

Black  Leg  (Bacterial). 

The  disease  appears  when  the  plants  are  quite  young  and  small.  The 
affected  plants  are  of  a  pale  color,  with  the  leaflets  rolled  inward  and 
the  shoots  unnaturally  straight.  The  stem  is  conspicuously  blackened 
below  ground,  or  in  some  cases  somewhat  above  ground,  especially  in 
moist  weather.    The  seed  tuber  decays  prematurely. 

This  trouble,  which  appears  to  be  due  to  a  definite  bacillus,  has  oc- 
cured  quite  extensively  in  southern  California. 

Do  not  plant  seed  potatoes  from  affected  fields.  Soak  the  seed  in  for- 
malin solution  as  for  scab.    Avoid  planting  in  affected  soil. 

Little  Potato. 

Clusters  of  abnormally  small  tubers  develop  near  the  surface  of  the 
ground  or  even  upon  the  stems  above  ground. 

Apparently  due  to  root  or  stem  diseases  which  cause  decay  of  the 
parts  below  ground.  May  be  caused  mainly  by  Rhizoctonia,  which  soil 
fungus  is  very  common  in  California.  In  the  latter  case  numerous 
small,  black  sclerotia,  the  resting  stage  of  the  fungus,  are  commonly  to 
be  found  clinging  to  the  surface  of  healthy  potatoes  of  normal  size,  with 
apparently  no  ill  effect.     Figure  81. 

Use  same  treatment  as  for  scab. 


Bulletin  218] 


CALIFORNIA    PLANT   DISEASES. 


1159 


Fig.  81. — Rhisoctonia  on  potato. 


1160  UNIVERSITY   OF    CALIFORNIA — EXPERIMENT   STATION. 

General  Directions  for  Potato  Planting. 

Use  seed  from  a  field  unaffected  by  disease  of  any  sort  and  plant  only 
potatoes  which  are  free  from  decay  and  any  internal  discoloration. 

Avoid  planting  on  land  where  potatoes  were  affected  the  previous  year 
with  any  disease  of  the  parts  below  ground. 

Before  cutting  the  seed  potatoes  soak  them  for  one  and  one  half  hours 
in  a  solution  of  one  pint  of  formalin  to  thirty  gallons  of  water. 

PRUNE.     See  Plum. 
Shrivels. 
The  fruit  becomes  discolored  on  one  side,  shrivels  and  dries  before 
maturity,  remaining  small  and  worthless. 

Prunes  are  grown  in  California  very  largely  without  irrigation,  and 
this  trouble  is  undoubtedly  due  to  a  lack  of  water.  It  occurs  particularly 
in  dry  seasons  when  the  winter  rains  cease  very  early.  Under  such 
conditions  the  water  supply  fails  early  in  the  season  and  the  fruit  has 
not  sufficient  moisture  for  its  full  development.  The  foliage  also  suffers 
from  the  same  cause,  many  of  the  leaves  fall,  red  spider  becomes  prev- 
alent, hastening  the  fall  of  the  leaves  and  further  weakening  the  tree, 
and  the  fruit  is  exposed  to  sunburn,  which  hastens  its  premature 
maturity. 

PUMPKIN. 
Mildew  (Erysiphe  cichoracearam) . 

This  white  powdery  mildew  often  covers  the  leaves  of  pumpkin  vines. 
Not  serious. 

Wilt    (Bacillus  tracheiphilus) . 

The  vines  wilt  and  die  from  no  apparent  cause.  A  decay  develops 
in  the  stem  which  appears  to  be  caused  by  a  bacterial  organism.  So  far 
as  investigated,  this  does  not  seem  to  agree  entirely  with  the  charac- 
teristics of  the  disease  caused  by  the  organism  named  above,  which 
occurs  in  other  parts  of  the  country. 

QUINCE. 
Blight  (Bacillus  amylovorus) .     See  Pear.     Not  serious. 

Little  Leaf.     See  Peach.     Figure  82. 
Black  Knot. 

Large  black  knots  or  swellings  develop  abundantly  on  the  trunk  and 
branches.  This  condition  is  so  common  and  characteristic  on  the  quince 
in  California  that  it  has  come  to  be  regarded  as  a  normal  one.  It  is  a 
fact  that  there  appears  to  be  no  particularly  bad  effect  from  such  knots, 
as  the  trees  continue  to  live  and  bear  fruit  in  an  apparently  healthy  con- 
dition. Whether  or  not  these  swellings  are  due  to  the  specific  organism 
of  root  knot  (Bacterium  tumefaciens)  has  never  been  determined. 


IIUU.ETIN218] 


CALIFORNIA    PLANT    DISEASES. 


1161 


Fig.  82. — Little  leaf  of  quince. 


1162 


UNIVERSITY    OF    CALIFORNIA — EXPERIMENT   STATION. 


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Bulletin  218]  CALIFORNIA  PLANT  DISEASES.  1163 


ROSE. 
Mildew  (Sphaerotheca  pannosa  and  S.  humuli).     Figures  83,  84  and  85. 

Roses  in  California  are  commonly  affected  with  two  different  powdery 
mildews  quite  different  in  appearance  from  one  another.  The  first 
named  is  seen  most  characteristically  on  the  hybrid  roses  and  is  partic- 
ularly severe  on  the  Crimson  Rambler.  It  forms  a  thick,  dense,  felty 
white  growth  upon  the  green  shoots,  buds,  and  young  leaves  more  than 
on  the  surface  of  the  older  leaves.  This  does  not  affect  the  tea  roses. 
The  latter  are  particularly  susceptible,  however,  to  the  second  fungus 
named,  which  produces  a  more  delicate  fungus  growth  upon  the  leaves 
and  blossoms  rather  than  the  stems,  giving  them  a  crinkled  appearance. 

The  most  effective  treatment  for  these  and  the  following  rose  troubles 
consists  in  spraying  the  bushes  occasionally  with  a  solution  of  sulphide 
of  potash  (liver  of  sulphur),  one  ounce  to  three  gallons  of  water.  Spray 
the  under  side  of  the  leaves  as  well  as  the  top  and  make  up  the  solution 
fresh  each  time  the  spraying  is  done.  If  the  bushes  are  also  affected 
with  plant  lice  an  addition  of  tobacco  extract  or  cheap  soap  may  be  made 
to  the  spray.  In  bad  cases  of  mildew  further  relief  may  be  obtained  by 
dusting  the  bushes  thoroughly  with  flowers  of  sulphur  while  they  are 
still  wet  with  the  spray. 

Different  varieties  vary  greatly  in  susceptibility,  and  the  ordinary 
grower  will  find  the  most  satisfaction  by  discarding  the  most  susceptible 
kinds  and  growing  others  which  are  less  liable  to  disease. 

Rust    (Phragmidium  subcorticium) .     Figure  86. 

Affects  the  hybrid  roses,  causing  the  leaves  to  turn  yellow  and  fall, 
with  black  or  bright  orange  pustules  of  rust  spores  on  the  under  side. 

See  Mildew. 

Black  Spot  (Actinonema  roscc). 

Produces  purplish  or  discolored  areas  of  considerable  size  on  the  sur- 
face of  the  leaves,  causing  them  to  drop. 

See  Mildew. 

Cane  Blight.     Figure  87. 

Affected  wood  turns  a  dark  purplish  or  black  color,  with  a  sharply 
defined  line  between  the  sound  and  diseased  bark. 

This  trouble  is  common  in  California  and  due  to  a  fungus  which  is 
apparently  undescribed  in  plant  disease  literature.  It  infects  stubs  left 
in  pruning  and  often  develops  down  into  the  main  branches,  seriously 
injuring  the  bushes. 

May  be  largely  avoided  by  proper  pruning. 


1164  UNIVERSITY   OF    CALIFORNIA — EXPERIMENT   STATION. 


Fig.  85. — Rose  mildew   (Sijhaerothcca  humuli) . 


Bulletin  21S] 


CALIFORNIA    PLANT    DISEASES. 


1165 


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1166 


UNIVERSITY   OF    CALIFORNIA EXPERIMENT   STATION. 


SORGHUM. 

Smut   (Sphacelotheca  sorghi  and  S.  reiliana). 

This  crop  is  affected  by  two  different  smut  fungi  in  California,  the 
former  developing  a  black,  dusty  mass  of  spores  in  place  of  the  seeds 
of  the  grain,  while  the  latter  breaks  out  in  swellings  on  the  plant  itself, 
containing  the  black,  smutty  spore  masses  like  corn  smut. 

Use  seed  from  fields  free  of  smut. 

STRAWBERRY. 
Leaf  Spot  (Sphaerella  fragarice).     Figure  88. 
This  fungus  produces  on  the  leaves  numerous  small  dead  spots  with 
dark  purple  margins. 


Fig.  88. — Leaf  spot  of  strawberry  (Sphaerella  fragariae). 

In  badly  affected  fields  mow  the  leaves  closely  and  burn  them. 
Spray  with  Bordeaux  mixture  if  the  trouble  is  serious  enough  to  war- 
rant this. 

Mildew  {Sphaerotheca  castagnei). 

A  white  surface  mildew.    Not  serious. 


Bulletin  218] 


CALIFORNIA   PLANT   DISEASES. 


1167 


SQUASH.     See  Pumpkin. 

SWEET  POTATO. 
Stem  Rot — Wilt  (Fusarium). 
The  plants  gradually  die  and  wither  away  in  the  field,  the  stem  and 
roots  being  affected  by  this  dry  rot  fungus. 

Use  seed  from  an  uninfested  locality  and  plant  on  fresh  land  as  far 
as  possible. 

Gather  and  burn  all  affected  vines. 

Black  Rot   (Ceratocystis  fimbriata). 

Characterized  by  black,  dry,  scabby 
patches  developing  on  the  potatoes  while 
they  are  in  the  ground. 

Do  not  use  seed  from  infested  fields  or 
plant  again  on  the  same  ground. 

Soft  Rot  (Rhizopus  nigricans).     Figure  89. 

A  soft  decay  of  the  potatoes  in  storage, 
caused  by  a  black  mold  which  appears  on 
the  surface. 

Handle  the  potatoes  carefully  while 
green  and  let  them  cure  or  dry  thoroughly 
before  storing.  Pack  in  dry  sand  for  long 
keeping. 

SYCAMORE. 

Blight   (Gloeosporium  nervisequum) . 

The  young  growth  is  killed  back  as 
though  by  frost.  This  fungus  affects  syca- 
more trees  quite  universally  just  after  they 
leaf  out  in  the  spring. 

No  practical  means  of  control,  except  by 
spraying  specimen  or  particularly  choice 
trees  with  Bordeaux  mixture  just  before 
they  leaf  out. 


Fig.     89. — Sweet     potato     rot 
{Rhizopus  nigricans). 


Mildew  (Microsphaera  sp.). 
A  powdery  mildew  has  been  found  in  nurseries  on  the  Sycamore. 

TOMATO. 
Damping  Off   (Rhizoctonia,  Fusarium.  Sclerotinia,  Botrytis).     Figure  90. 

Young  plants  in  the  seed  bed  decay  at  the  surface  of  the  ground  and 
die  away  in  large  numbers.  Much  worse  in  damp,  cloudy  weather  and 
sometimes  difficult  to  control  under  such  conditions.  Caused  by  various 
fungi.    The  trouble  is  checked  by  bright  sunlight  and  dry  weather. 

Make  the  seed  bed  soil  as  sandy  as  possible. 


1168 


UNIVERSITY    OF    CALIFORNIA — EXPERIMENT    STATION. 


Avoid  excessive  watering  when  the  weather  is  favorable  to  this 
trouble;  water  only  in  the  morning  and  on  sunny  days  so  far  as  pos- 
sible.    Give  the  plants  plenty  of  ventilation  and  fresh  air. 

Summer  Blight    (Fusarium). 
Occasional  plants  here  and  there  in  the  field  gradually  turn  yellow, 

sicken  and  die,  after  reaching  consider- 
able size.  A  dry  rot  is  found  in  the  stem 
and  roots,  caused  by  a  fungus.  This 
fungus  does  not  infest  the  soil  in  the 
field  and  the  disease  may  be  abundant 
one  year  and  totally  absent  the  next 
year  in  the  same  field.  Affected  plants 
sometimes  do  not  show  the  fungus  until 
in  the  last  stages,  and  there  is  some 
doubt  as  to  the  identity  or  cause  of  this 
trouble.  Plants  may  become  infested  in 
the  seed  bed  under  conditions  favorable 
to  damping  off.  It  is  possible  that  two 
different  diseases  are  confused  in  this 
trouble. 

Keep  the  seedlings  as  free  from  damp- 
ing off  as  possible  and  use  only  the  best 
plants  for  planting  in  the  field.  Select 
seed  from  healthy  plants. 

See  Bulletin  175,  California  Experi- 
ment Station. 

Winter  Blight  {Phytophthora  infestans). 
Figures  91  and  92. 

The   leaves    and   stems   are   suddenly 
blackened  and  killed  and  the  fruit  spots 
and  decays.     The  whole  effect  is  quite 
similar  to  that  of  frost.     Caused  by  the 
potato  blight  fungus.    Never  occurs  dur- 
ing the  summer,  but  occasionally  comes 
on  to  a  disastrous  extent  on  the  winter 
shipping  crop  following  early  fall  rains,   or  in   early  spring   plants. 
Spray  with  Bordeaux  mixture  immediately  following  rain. 
See  Bulletin  175,  California  Experiment  Station. 

Blossom  End  Rot.     Figure  93. 

The  end  of  the  tomato  becomes  discolored  and  affected  with  a  dry 

rot  which  spreads  to  a  greater  or  less  extent.     Tomatoes  of  all  sizes  are 

affected,  particularly  those  which  are  half  grown.    No  definite  cause  has 

been  found  for  this  trouble,  which  varies  in  abundance  from  year  to 


Fig. 


90. — Damping  off  of  tomato 
seedlings. 


Bulletin  218] 


CALIFORNIA    PLANT    DISEASES. 


1169 


Fig.  91. — Winter  blight  of  tomato  fruit  (Phytophthora  infestans), 


1170 


UNIVERSITY   OF    CALIFORNIA — EXPERIMENT   STATION. 


year.     Apparently  worse  on  dry  ground  where  the  vines  do  not  receive 
regular  irrigation. 


Fig.  92. — Winter  blight  of  tomato  leaf  (Phytophthora  infestans) , 


Fig.  93. — Blossom  end  rot  of  tomato. 
Stem  Rot   (Sclerotinia  libertiana). 

A  dry  rot  of  the  stem  and  wilting  of  the  vine.     Found  only  in  green- 
houses.   Not  serious. 


Bulletin  21S] 


CALIFORNIA   PLANT   DISEASES. 


1171 


Leaf  Spot  (Scptoria  lycopersici) . 
Small  dead  spots  appear  on  the  leaves.     Not  common  or  serious. 
Found  mostly  in  seed  beds. 

Root  Knot  (Nematode). 
Galls  or  swellings  appear  all  over  the  roots  and  the  plants  sicken  and 
die.     Infection  takes  place  in  the  seed  bed.     Carefully  discard  affected 
plants  in  field  planting  and  change  the  soil  in  infested  beds. 

TURNIP.     See  Cabbage. 


Fig.  94. — Leaf  spot  of  vetch  (Colletotrichum  sp.). 

VETCH. 

Leaf  Spot.     Figure  94. 
Small  black  spots  appear  on  the  leaves  and  the  whole  plant  is  more  or 
less  killed.     Does  some  damage  on  vetch  planted  for  a  cover  crop ; 
usually  associated  with  the  cottony  mold  fungus,  Sclerotinia.     Caused 
by  a  fungus,  probably  a  species  of  Collet otrichum. 


1172 


UNIVERSITY    OF    CALIFORNIA — EXPERIMENT    STATION. 


WALNUT. 

Bacteriosis    (Pscudomonas  juglandis).     Figures  95,   96   and  97. 

Blight. 
Causes  a  black  spotting  on  the  surface  of  the  young  nuts,  many  of 
which  drop  prematurely.  Affected  nuts  which  reach  full  size  have  the 
contents  blackened  and  spoiled.  The  shoots  are  also  affected  with  the 
production  of  black,  canker-like  areas,  most  of  which  heal  out  as  the 
wood  hardens,  leaving  wounds  and  cankers  of  considerable  size.  Many 
of  the  small  fruit  spurs  and  twigs  are  entirely  killed,  but  the  disease 


Fig.  95. — Walnut  blight  on  nuts  (Pseudomonas  juglandis) . 

does  not  kill  large  limbs  or  whole  trees.  The  leaves  are  also  affected  in 
black  spots. 

The  disease  varies  in  abundance  from  year  to  year,  being  most  preva- 
lent in  seasons  with  much  fog  and  moisture  late  in  the  spring. 

No  practical  remedy  has  been  found  for  this  disease,  but  the  problem 
has  been  largely  solved  by  the  development  of  immune  varieties.  Such 
trees  are  now  available  to  a  limited  extent  and  must  soon  supplant  the 
present  plantings  of  seedlings  or  susceptible  kinds. 

Some  control  may  possibly  be  obtained  by  spraying  with  Bordeaux 
mixture  or  sulphur  sprays  just  before  the  buds  open.  The  expense  of 
spraying  walnut  trees  thoroughly  is  so  great,  and  so  much  time  is  re- 
quired to  thoroughly  cover  trees  of  this  size,  that  we  have  no  faith  in  a 
satisfactory  solution  of  the  walnut  blight  problem  along  this  line. 


Bulletin  218] 


CALIFORNIA    PLANT    DISEASES. 


1173 


On  old  groves  liberal  fertilization  with  nitrogenous  fertilizers,  to- 
gether with  the  use  of  green  manure  crops,  will  go  far  towards  making 
up  for  the  losses  caused  by  the  disease. 

Most  walnut  groves  would  be  benefited  by  more  irrigation  than  they 


Fig.  96. — Lesions  on  blighted  walnut  twigs  (Pseudomonas  juglandis) . 

receive  at  present,  particularly  during  the  winter  and  in  the  fall  after 
the  crop  is  harvested. 

See  Bulletin  203,  page  24,  California  Experiment  Station. 

Trunk  Rot  {Schizophyllum  commune).  Figure  Go. 
The  trunk  or  main  branches  rot,  with  a  production  of  small,  white 
bracket  toadstools  on  the  surface  of  the  affected  wood.  This  fungus 
does  not  affect  sound  trunks,  but  follows  deep  wounds,  bruises,  heavy 
cutting,  sunburn  or  other  injuries.  The  wood  of  the  English  walnut 
is  particularly  susceptible  to  this  form  of  decay. 


1174 


UNIVERSITY   OF    CALIFORNIA EXPERIMENT    STATION. 


Fig.   97. — Blighted  walnut  twigs  (Pseudomonas  juglandis) . 


Bulletin  218] 


CALIFORNIA   PLANT   DISEASES. 


1175 


All  severe  cuts  or  wounds  should  be  carefully  covered  with  grafting 
wax  to  allow  healing  over  without  decay.  In  top-grafting  walnut  trees 
this  should  be  given  special  attention  or  serious  decay  may  follow. 

Sun  Burn.  Figure  98. 
Serious  damage  is  sometimes  caused  from  this  source,  both  on  the 
fruit  and  the  tree.  In  the  latter  case  the  trunk  is  usually  affected,  dead 
areas  developing  in  the  bark  on  the  sunny  side.  This  originates  mostly 
in  winter  when  the  nights  are  cold  and  the  days  bright  and  sunny.  Not 
usually  serious  on  thrifty  trees  growing  in  good  soil.     Black  walnut 


Fig.  98. — Walnuts  affected  by  sun  burn. 

trunks  with  rough  bark  are  not  affected  by  sun  burn,  so  that  trees 
grafted  high  on  such  trunks  are  immune. 

On  the  fruit  the  sun  sometimes  has  a  disastrous  effect,  causing  a 
blackening  and  burning  of  the  husk  on  one  side  during  extremely  hot 
weather  in  summer.  The  meat  is  also  blackened,  and  the  husk  sticks 
to  the  shell  so  that  separation  is  difficult  and  a  black  spot  is  left.  Thrifty 
trees  are  less  affected,  particularly  when  supplied  with  an  abundance 
of  moisture  at  the  root.  Individual  trees  or  varieties  vary  in  suscepti- 
bility to  this  trouble,  and  this  quality  should  be  considered  in  planting 
in  localities  where  trouble  from  sunburn  is  likely  to  occur. 

Perforation.  Figure  99. 
The  shell  fails  to  develop  properly,  being  only  partially  formed,  with 
numerous  openings  and  thin  places.  This  appears  to  be  simply  a  lack 
of  development  due  to  climatic  conditions  and  occurs  in  seasons  with  a 
dry  spring  and  a  dry,  hot  summer.  Seems  worse  on  trees  attacked  by 
aphis. 


1176 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION. 


Erinose. 


Blister-like  swellings  appear  on  the  leaves,  sometimes  becoming  very 
abundant.  This  trouble  is  caused  by  an  insect,  so  minute  that  it  is  not 
visible  to  the  eye. 

Not  serious  or  requiring  treatment. 


Fig.  99. — Walnut  perforation. 

Die-Back.     Figure  100. 

The  limbs  die  back  from  the  ends,  sometimes  for  only  a  short  dis- 
tance and  sometimes  down  to  the  main  forks  of  the  tree.  All  the  limbs 
or  only  a  part  of  them  may  be  affected.  Two  general  types  of  die-back 
may  be  distinguished,  one  on  the  old  trees,  particularly  "hard  shells," 
which  die  back  slowly  all  over  the  top,  and  another  in  young  trees  from 
two  to  ten  years  old,  which  die  back  suddenly  during  a  single  winter  in 
part  or  all  of  the  limbs,  or  sometimes  the  whole  tree  dies  back  clear  to 
the  ground. 

The  former  type  of  die-back  affecting  old  trees  occurs  mostly  on  light 
soils  where  the  trees  are  getting  old  and  the  roots  find  insufficient  moist- 


BULLETIN  21  S  | 


CALIFORNIA    PLANT    DISEASES. 


1177 


ure.  Such  dying  back  is  also  hastened  by  lack  of  cultivation,  irrigation 
and  plant  food,  which  lack  becomes  more  pronounced  as  the  trees  grow 
older  and  the  tops  and  roots  more  crowded.  The  only  remedy  for  this 
trouble  is  to  thin  out  the  trees  where  they  are  too  closely  planted  and 
give  the  soil  better  care.  Most  of  these  old  hard  shell  orchards,  even  at 
best,  have  now  become  so  unprofitable  and  undesirable  as  to  make  it 
seem  better  for  the  owners  to  cut  down  the  trees  and  use  the  land  for 
some  other  purpose. 

The  second  form  of  die-back  mentioned,  that  occurring  in  young  trees 
which  have  formerly  been  thrifty,  killing  them  down  to  the  forks  or 
even  to  the  ground,  is  a  very  serious  matter  at  present  in  some  districts. 
The  trouble  shows  usually  to  a 
greater  extent  in  a  certain  por- 
tion of  the  orchard  or  in  certain 
orchards  worse  than  in  others 
near  by.  It  developed  more  ex- 
tensively in  the  spring  of  1911 
than  ever  before,  when  a  great 
many  trees  which  had  seemed 
healthy  and  vigorous  the  pre- 
vious fall  were  found  to  be  al- 
most entirely  dead  in  the  spring. 
Affected  trees  failed  to  leaf  out 
at  the  proper  time  and  more  or 
less  of  the  top  proved  to  be  either 
entirely  dead  or  developed  very 
slowly  later  in  the  season.  Such 
trees  often  threw  out  new  growth 
or  suckers  toward  the  base, 
which  made  a  very  vigorous 
growth,  while  the  tops  were  dead 
or  very  slow  in  coming  out.  The 
leaves  which  finally  developed 
from  the  affected  limbs  had  a  yellow,  sickly  appearance. 

This  trouble  is  more  or  less  the  same  as  that  described  under  wralnut 
'Yellows,"  and  evidently  has  been  caused  by  the  abnormally  dry  sea- 
son of  1910.  The  disease  is  practically  the  same  in  its  nature  as  that 
described  as  the  "Little  Leaf"  of  the  peach  and  shows  similar  relations. 
Trees  standing  over  coarse,  dry  subsoil  or  those  which  had  for  any  rea- 
son become  drier  than  usual  during  the  fall  of  1910  showed  the  trouble 
the  worst.  Young  trees  under  ten  years  of  age  showed  the  trouble 
worse  than  older  ones.  It  is  a  common  practice  in  some  of  the  worst 
affected  districts  to  grow  alfalfa  between  the  walnut  rows  and  in  groves 
or  portions  of  groves  which  for  this  reason  became  drier  than  the  aver- 


Fig/100. — Die-back  of  walnut. 


1178  UNIVERSITY   OF    CALIFORNIA — EXPERIMENT   STATION. 

age  late  in  1910  the  trouble  has  been  worse.  Even  in  some  fairly  heavy 
soils  the  packing  of  the  surface  on  account  of  several  years'  irrigation 
and  handling  of  alfalfa  prevented  the  moisture  reaching  the  subsoil  and 
thus  the  same  effect  was  produced.  Frost  was  also  responsible  to  a 
greater  or  less  extent  for  the  dying  back  of  trees  in  dry  ground. 

Trees  affected  in  this  way  should  be  pruned  back  to  good  live  wood, 
if  not  too  far  gone,  and  it  is  to  be  expected  that  a  new  top  will  soon  be 
produced.  By  proper  attention  to  irrigation  late  in  the  season,  espe- 
cially in  dry  years,  it  is  not  to  be  expected  that  the  trouble  will  occur 
again  save  in  soils  most  unsuitable  for  walnuts  on  account  of  coarse 
subsoil  near  the  surface.  We  may  say  here  that  in  choosing  crops  for 
interplanting  walnuts,  it  is  not  desirable  to  let  the  ground  remain  in 
alfalfa  too  long  unless  an  abundant  water  supply  is  available,  and  one 
can  be  sure  by  actual  examination  that  the  soil  is  sufficiently  moist  at 
all  times,  both  for  the  alfalfa  and  for  the  trees.  In  any  event,  it  is 
ordinarily  best  to  leave  a  cultivated  strip  at  least  eight  feet  wide  on 
each  side  of  the  tree  row,  and  as  the  trees  grow  older  it  is  better  to  plow 
out  the  alfalfa  and  grow  some  annual  crop  which  will  receive  regular 
cultivation,  as  well  as  irrigation. 

Yellows. 
Spindling,  yellow  shoots  develop  which  usually  die  back  from  the 
tip.  All  degrees  of  the  trouble  may  occur  from  slightly  unnatural 
yellowing  and  slenderness  of  the  normal  shoots  to  the  production  of 
masses  of  small,  yellow  shoots,  with  continual  dying  back.  This  affects 
the  English  walnut,  and  is  even  more  pronounced  on  the  Northern 
California  black  walnut  in  certain  seasons  and  places.  It  has  been 
abundant  even  on  black  walnut  trees  of  large  size  in  some  parts  of 
northern  California  during  the  last  two  or  three  years,  and  very  preva- 
lent in  nursery  trees  of  the  northern  California  species  grown  in  the 
southern  part  of  the  State.  At  the  same  time  and  in  the  same  nurseries 
seedlings  of  the  southern  California  black  walnut  have  never  shown  the 
slightest  indication  of  this  trouble.  This  disease  appears  to  be  the 
same  which  affects  the  peach  (which  see),  and  also  to  some  extent  the 
pecan,  apple,  and  many  other  trees.  It  is  probably  due  to  a  climatic  or 
soil  condition  rather  than  to  any  parasite.  Conditions  which  result  in 
sour  sap  and  similar  troubles  in  the  stone  fruits  seem  to  be  related  to 
this  disease,  and  it  is  very  likely  due  to  a  disturbance  of  the  dormant  or 
resting  condition  through  which  these  trees  normally  pass  during  the 
winter.    Also  seems  to  be  connected  with  lack  of  rain  or  irrigation  late 

in  the  season. 

Crown  Gall — Black  Knot.     Figure  101. 

Walnut  trees  are  affected  in  some  instances  with  large  knots  or 
cankers  on  the  trunk  just  below  ground  or  a  slight  distance   above 


Bulletin  218] 


CALIFORNIA   PLANT   DISEASES. 


1179 


ground.  This  trouble  is  not  a  common  one,  but  seems  to  occur  in  some 
districts  more  than  others.  Whether  such  knots  are  due  to  the  real 
crown  gall  organism  (Bacterium  tumefaciens)  has  never  been  de- 
termined, but  their  appearance  leads  one  to  suspect  that  they  originate 
from  infection  of  scars  or  wounds  on  the  trunk  by  this  parasite.  Known 
only  upon  the  English  walnut. 

As  soon  as  the  trouble  appears  cut  out  the  diseased  tissue,  disinfect 
with  strong  bluestone  solution  and  paint  over  the  wound. 


Fig.  101. — Black  knot  on  walnut  trunk  (Bacillus  tumefaciens) . 

Crop  Failure. 
It  is  a  very  noticeable  fact  in  connection  with  the  California  walnut 
industry  that  the  total  product  of  the  groves  of  the  State  is  not  mate- 
rially increasing,  although  the  acreage  has  multiplied  many  times  during 
recent  years.  This  is  due  to  a  very  general  condition  of  poor  produc- 
tion in  the  large  walnut-growing  sections  of  the  southern  portion  of  the 
State.  The  older  groves,  although  by  no  means  at  an  age  when  they 
should  be  deteriorating,  show  very  little  tendency  to  increase  their 
yield,  and  in  many  cases  are  gradually  going  back.  The  quality  and 
size  of  the  nuts,  as  well  as  the  quantity,  is  also  a  source  of  complaint. 
Many  of  the  nuts  which  mature  are  empty  or  poorly  filled  with  shriveled, 
light  weight  meat,  giving  the  nut  when  cracked  an  unattractive  appear- 
ance. 


1180  UNIVERSITY    OF    CALIFORNIA — EXPERIMENT    STATION. 

Trouble  of  this  nature  is  quite  commonly  attributed  to  walnut  blight, 
with  which  disease,  however,  it  has  nothing  to  do.  There  is  probably 
no  one  cause  or  reason  for  this  condition.  It  is  due,  generally  speaking, 
to  a  loss  of  vitality  in  the  trees,  brought  about  mostly  by  unavoidable 
mistakes  made  in  planting  when  the  industry  was  new  and  experience 
in  walnut  growing  very  limited.  In  the  first  place,  all  the  older  groves 
were  planted  with  the  trees  too  close  together.  At  the  common  distance 
of  forty  feet  the  branches  begin  to  touch  before  the  trees  are  ten  years 
old,  and  by  the  time  they  reach  full  bearing  age,  the  ground  is  com- 
pletely shaded  and  the  tops  of  the  trees  form  a  solid  mass  throughout. 
This  condition  is  extremely  unfavorable  to  walnut  production,  and  as 
the  groves  grow  older  is  the  cause  of  more  and  more  lessening  of  the 
crop. 

Another  factor  in  walnut  deterioration  has  been  the  common  idea 
that  these  trees  require  very  little  cultivation,  irrigation,  or  fertilization 
and  the  very  irregular  attention  which  they  have  received  in  this  respect. 
It  is  true  that  many  walnut  trees  exist  which  receive  no  cultivation 
whatever  and  produce  very  good  crops.  Such  trees,  however,  usualty 
stand  out  by  themselves  with  full  exposure  on  all  sides,  and  moreover, 
while  the  ground  about  them  is  not  cultivated,  it  is  at  least  subject  to 
uniform  conditions.  The  walnut  tree  seems  to  particularly  resent  rad- 
ical changes  in  soil  treatment.  It  may  do  well  with  no  cultivation  and 
will  do  better,  other  things  being  equal,  with  good  cultivation,  but  it 
is  decidedly  injured  by  irregular  treatment  in  this  respect. 

Another  feature  of  the  situation  is  the  fact  that  all  our  older  groves 
are  seedling  trees,  growing  thus  on  their  own  roots.  The  English  wal- 
nut root  of  the  type  most  commonly  grown  in  southern  California  is 
thrifty  and  vigorous  when  soil  conditions  are  very  favorable,  but  has 
little  ability  to  withstand  hardship.  Many  of  the  present  walnut  groves 
have  been  planted  on  soil  which  for  one  reason  or  another  is  not  well 
adapted  to  this  root,  and  as  a  result  the  trees  gradually  fail  as  they 
grow  older. 

Again,  the  inherent  nature  of  the  trees  in  regard  to  quality  and 
quantity  of  production  is  responsible  to  a  considerable  extent  for  the 
present  unsatisfactory  condition.  Almost  every  walnut  tree  over  ten 
years  of  age  in  Santa  Barbara,  Ventura,  Los  Angeles,  and  Orange 
counties  is  of  the  type  known  as  the  Santa  Barbara  soft  shell  seedling. 
These  have  all  descended  from  a  few  trees  of  the  original  planting  of 
Joseph  Sexton  and  have  in  most  cases  been  planted  with  no  discrimina- 
tion or  selection  of  the  nuts.  As  a  result  of  this  the  type  has  degener- 
ated to  a  marked  extent  and  a  large  proportion  of  the  present  trees  are 
decidedly  inferior  inheritently  to  their  original  parents. 

In  addition  to  all  this,  the  climatic  conditions  of  the  last  two  or 


Bulletin  218]  CALIFORNIA  PLANT  DISEASES.  1181 

three  years  have  been  such  as  to  have  a  decidedly  unfavorable  effect 
upon  walnuts,  as  described  in  other  portions  of  this  bulletin.  The  case 
is,  therefore,  not  altogether  hopeless,  since  it  is  to  be  expected  that  even 
under  present  conditions  we  may  have  better  walnut  seasons  and  crops 
than  those  of  the  past  few  years.  With  better  and  more  regular  cultural 
care  of  the  orchards  which  is  now  coming  into  practice,  there  is  still  more 
hope  for  the  future.  Growers  are  beginning  to  realize  that  some  of  the 
attention  which  they  give  their  orange  and  lemon  groves  might  not  be 
wasted  upon  walnuts. 

The  faults  outlined  above  may  be  counteracted  to  a  considerable  ex- 
tent by  thinning  out  the  closely  planted  trees,  either  by  removing  a  por- 
tion of  the  tops  or  taking  out  some  of  the  trees  bodily,  and  by  giving 
the  groves  cultivation,  irrigation,  and  fertilization  along  rational  lines. 
The  fact  is  apparent,  however,  that  the  present  seedling  walnut  groves 
have  had  their  day  and  that  they  will  gradually  disappear  just  as  the 
seedling  apple,  the  seedling  orange  and  all  other  fruits  of  the  same 
nature  are  gradually  supplanted  by  more  desirable,  definite  varieties. 
The  real  hope  of  the  walnut  industry  lies  in  the  future,  and  is  based 
upon  an  entirely  new  start  along  the  lines  just  mentioned.  Upon  this 
basis  there  is  absolutely  no  doubt  but  that  the  walnut  will  again  come 
into  its  own  and  prove  one  of  our  most  attractive  and  profitable  crops. 
A  complete  bulletin  upon  walnut  culture  in  all  of  its  phases  is  now 
under  preparation  by  the  senior  writer. 

WATERMELON. 

Wilt  (Fusarium). 
The  vines  wilt  and  die  with  a  dry  rot  of  the  stem  and  leaves.    Caused 
by  a  fungus  which  infests  the  soil  and  lives  there  from  year  to  year. 
Plant  on  new  soil.    Resistant  varieties  are  being  developed. 

WHEAT. 

Closed  Smut  (Tilletia  foetans).     Figure  102. 
The  grains  are  converted  into  a  black  substance  which  does  not  scatter 
out  loosely  as  in  the  next.    Affected  grains  have  a  disagreeable  odor. 
Use  seed  treatment  as  for  barley  smut. 

Loose  Smut  (Ustilago  tritici).     Figure  102. 

The  kernels  and  chaff  are  converted  into  a  black,  powdery  mass,  which 
blows  away  before  harvest  time,  leaving  the  bare  stalks. 

Use  the  hot  water  treatment  as  for  barley  if  this  form  of  smut  is 
particularly  bad. 

Rust  (Puccinia  graminis). 

The  rust  appears  as  an  orange-red  powder  on  the  leaves,  later  turning 
black.    Wheat  fields  are  sometimes  badly  injured  when  the  weather  is 
10— Bul.  218 


1182 


UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION. 


moist  and  favorable  to  the  rust.     Some  varieties  are  considerably  re- 
sistant. 

Yellow  s — Wi  n  teri  ng  . 

Wheat,  as  well  as  other  grains,  sometimes  shows  in  the  spring  a  yellow- 
ing and  discoloration  of  the  leaves  with  no  apparent  specific  cause. 


Fig.   102. — Closed  and  loose  smut  of  wheat   (Tilletia  foetans  and 

Ustilago  tritici). 

Sometimes  the  whole  field  shows  this  condition  so  decidedly  as  to  have 
the  appearance  of  being  badly  injured.  The  trouble  appears  to  be  due 
to  climatic  conditions,  producing  a  disturbance  in  the  growth  of  the 
plant.  The  yellowing  usually  disappears  in  the  spring  and,  if  condi- 
tions are  favorable,  the  plants  regain  their  normal  appearance. 


Bulletin  2183  CALIFORNIA  PLANT  DISEASES.  1183 

FUNGICIDES. 

The  following  are  the  chief  substances  used  for  the  control  of  plant 
diseases  by  spraying,  dipping,  disinfecting,  etc.  It  should  be  clearly 
understood  that  all  control  of  this  nature  must  be  accomplished  entirely 
by  prevention  rather  than  cure.  In  other  words,  these  fungicides 
where  they  are  to  be  effective  must  be  applied  for  the  purpose  of  poison- 
ing and  killing  the  spores  or  germs  of  the  parasites  and  thus  preventing 
their  further  spread  and  development. 

bluestone.     (Copper  Sulphate.) 

This  material  comes  in  the  form  of  large,  hard,  blue  crystals,  and  is 
used  in  large  quantities  in  fungicidal  work,  as  the  basis  of  Bordeaux 
mixture.  The  crystals  dissolve  readily  in  hot  water  and  more  slowly  in 
cold.  If  thrown  into  the  water  and  allowed  to  sink  to  the  bottom  they 
soon  form  there  a  concentrated  solution  and  only  a  small  part  of  the 
material  is  dissolved.  For  this  reason  it  is  necessary  to  either  stir  the 
water  frequently  or  suspend  the  bluestone  in  a  sack  or  basket  so  that 
it  just  dips  under  the  surface.  This  substance  is  extremely  caustic  to 
vegetation  when  used  alone,  and  is,  therefore,  commonly  combined  with 
lime  in  Bordeaux  mixture. 

A  plain  solution  of  bluestone  and  water  of  about  3  pounds  to  50  gal- 
lons may  be  used  during  the  winter  time  on  fruit  trees  to  remove  moss, 
etc.,  from  the  bark.  This  solution  would  be  extremely  disastrous  to 
green  leaves. 

LIME. 

This  material  in  the  form  called  "quick-lime"  or  "stone-lime,'  is 
mainly  useful  in  fungicidal  work  as  an  ingredient  of  Bordeaux  mixture. 
For  this  purpose  it  must  be  in  a  fresh,  hard  condition  and  not  in  the 
least  air-slaked. 

Hydrated  lime,  a  form  which  is  coming  considerably  into  use,  consists 
of  lime  which  has  been  slaked  with  a  small  amount  of  water  and  then 
ground  to  a  fine  powder.  In  this  condition  it  can  not  air  slake,  but  re- 
tains its  quality  indefinitely.  This  form  of  lime  is  being  used  to  some 
extent  for  making  Bordeaux  mixture  and  quite  extensively  as  a  basis 
of  dust  sprays. 

sulphur. 

This  in  a  finely  powdered  condition  is  used  extensively  in  the  control 
of  plant  diseases,  particularly  for  surface  mildews  and  the  like.  Sul- 
phur acts  in  these  cases  through  its  gaseous  fumes,  which  are  produced 
when  the  hot  sun  shines  upon  it.  For  such  purposes  the  sulphur  should 
be  in  as  finely  divided  a  condition  as  possible  and  this  is  best  obtained 
in  the  form  known  as  flowers  of  sulphur  or  sublimed  sulphur.    Ground 


1184  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION. 

sulphur  is  to  be  had  in  various  degrees  of  fineness,  but  should  never  be 
used  for  application  to  plants  except  in  the  very  finest  condition.  The 
sublimed  form  is  somewhat  more  expensive  per  pound,  but  much  bulkier, 
and  therefore  no  more  expensive  in  the  end.  When  used  in  liquid  sprays 
where  cooking  takes  place  and  the  sulphur  becomes  dissolved,  the 
cheaper,  coarser  forms  may  be  used. 

COPPER  CARBONATE. 

This  material  is  used  to  a  limited  extent  in  the  form  of  a  solution  in 
ammonia  and  water  in  the  case  of  spraying  fruit,  flowers,  ornamentals, 
etc.,  where  Bordeaux  mixture  is  objectionable  on  account  of  its  disfigur- 
ing effect.  This  ammoniacal  copper  carbonate  is  prepared  in  the  follow- 
ing manner : 

Copper  carbonate 6  ounces 

Strong  ammonia 3  pints 

Water 50  gallons 

Make  a  paste  of  the  copper  carbonate  with  a  little  water  and  add  to 
this  the  ammonia  diluted  with  about  two  gallons  of  water.  Stir  vigor- 
ously and  continue  to  add  the  ammonia  until  all  the  copper  is  dissolved. 
Then  dilute  to  50  gallons. 

potassium  sulphide.  (Liver  of  Sulphur.) 

This  material  comes  in  the  form  of  a  greenish-yellow  solid.  Used 
particularly  in  a  solution  of  1  ounce  to  3  gallons  of  water  for  the  con- 
trol of  surface  mildews.  Both  the  solid  and  the  solution  deteriorate  on 
standing  exposed  to  the  air. 

FORMALIN. 

This  is  a  clear  liquid  consisting  of  a  gas  dissolved  in  water.  Commer- 
cial formalin  should  have  a  strength  of  40  per  cent  and  the  formula 
given  below  is  based  upon  this  concentration.  In  buying  formalin  par- 
ticular care  should  be  taken  to  see  that  the  material  purchased  is  a 
40  per  cent  solution.  One  pint  dissolved  in  thirty  gallons  of  water  is 
used  for  soaking  seed  potatoes  in  the  control  of  scab  and  for  grain  in 
controlling  smut. 

CORROSIVE  SUBLIMATE. 

This  is  a  white,  extremely  poisonous,  solid  material  which  may  be 
bought  most  conveniently  in  the  form  of  tablets.  It  is  used  particularly 
for  disinfection  after  cutting  out  pear  blight,  dissolved  in  water  in  a 
strength  of  1-1000.  The  tablets  may  be  obtained  in  a  size  convenient  for 
making  this  strength.  This  material  is  particularly  poisonous  to  ani- 
mal life  and  should  not  be  carelessly  used. 


Bulletin  218]  CALIFORNIA  PLANT  DISEASES.  1185 

BORDEAUX  MIXTURE. 

Copper  sulphate  (Milestone) 5  pounds 

Quick-lime   (good  stone  lime) 6  pounds 

Water 50  gallons 

Put  the  bluestone  in  a  sack  and  hang  so  it  will  be  suspended  just 
under  the  surface  of  a  barrel  of  water  over  night,  or  dissolve  in  hot 
water.  Use  one  gallon  of  water  to  one  pound  of  bluestone.  Slake  the 
lime  in  a  separate  barrel,  using  just  enough  water  to  make  a  smooth,, 
clean,  thin  whitewash.     Stir  this  vigorously.     Use  wooden  vessels  only. 

Fill  the  spray  tank  half  full  of  water,  add  one  gallon  of  bluestone 
solution  for  each  pound  required,  then  strain  in  the  lime  and  the 
remainder  of  the  water  and  stir  the  mixture  thoroughly.  Do  not  mix 
the  solution  hot. 

For  extensive  work,  large  amounts  of  bluestone  and  lime  may  be  pre- 
pared in  advance  in  separate  receptacles,  making  stock  solutions  of 
definite  strength.  (One  pound  to  the  gallon  is  convenient.)  Always 
dilute  well  before  mixing. 

The  formula  may  be  varied  according  to  conditions,  using  from  3  to 
8  pounds  of  bluestone  to  50  gallons  of  water  and  an  equal  amount  or 
slight  excess  of  lime.  Use  the  stronger  mixture  in  rainy  weather. 
Keep  the  mixture  constantly  agitated  while  applying. 

Recently,  the  so-called  "hydrated"  lime  has  been  used  to  a  con- 
siderable extent  in  making  Bordeaux.  Chemically,  the  hydrated  lime 
is  entirely  satisfactory  for  making  Bordeaux  mixture,  and  it  is  some- 
what more  convenient  for  use  than  stone  or  quick  lime.  The  same  quan- 
tities should  be  employed  as  with  the  latter.  Objection  has  been  made 
to  hydrated  lime  in  some  quarters  on  the  ground  that  Bordeaux  mixture 
thus  prepared  settles  more  readily  and  has  a  coarser  consistency.  We 
are  not  prepared  to  state,  however,  that  this  is  a  general  fault  of 
hydrated-lime  Bordeaux. 

In  using  large  quantities  of  Bordeaux  mixture  or  any  other  fungicide 
it  is  very  convenient  to  place  tanks  upon  an  elevated  platform  to  which 
water  is  piped.  The  various  solutions  can  then  be  prepared  upon  this 
platform  and  discharged  by  gravity  into  a  spray  tank.  In  the  case  of 
Bordeaux  mixture  it  is  advisable  to  run  the  diluted  bluestone  and  lime 
solution  into  a  single  trough  and  let  them  drop  from  this  into  a  spray 
tank,  as  in  this  way  a  more  complete  mixture  is  secured. 

CAUSTIC  SODA  AND  POTASH. 

Either  of  these  substances  may  be  used  for  spraying  dormant  trees 
in  winter,  dissolved  in  water  in  the  proportion  of  1  pound  to  10  gallons. 
This  is  effective  in  removing  moss,  lichens,  etc.,  from  trees  and  also  has 
some  fungicidal  value  in  certain  cases.     These  materials  are  also  used 


1186  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION. 

combined  with  sulphur  in  liquid  sprays  in  which  the  sulphur  goes  into 
solution. 

SULPHUR  SPRAYS. 

Quick-lime 20  pounds 

Ground  sulphur 15  pounds 

Water 50  gallons 

Slake  the  lime  with  hot  water  in  a  large  kettle,  add  the  sulphur  and 
stir  well  together.  After  the  violent  slaking  subsides  add  more  water 
and  boil  the  mixture  over  a  fire  for  at  least  one  hour.  After  boiling 
sufficiently  strain  into  the  spray  tank  and  dilute  with  water  to  the 
proper  strength.  If  a  steam  boiler  is  available  this  mixture  may  be 
prepared  more  easily  on  a  large  scale  by  cooking  in  barrels  into  which 
steam  pipes  are  introduced.  This  mixture  can  not  be  applied  safely 
except  during  the  winter  Avhen  the  trees  are  dormant. 

SELF-BOILED  LIME-SULPHUR. 

The  heat  generated  by  the  lime  in  slaking  is  in  itself  sufficient  to 
dissolve  a  considerable  quantity  of  sulphur  and  a  mixture  may  be  pre- 
pared in  this  way  which  is  quite  satisfactory  for  fungicidal  purposes. 
This  method  has  been  in  use  for  several  years  in  California,  as  described 
in  Bulletin  163  of  the  California  Experiment  Station.  The  lime  is 
placed  in  a  tight  cask  instead  of  a  kettle,  and  over  it  is  poured  the 
sulphur  mixed  into  a  thin  paste  with  hot  water.  Ten  or  fifteen  gallons 
of  boiling  water  are  then  added  and  the  cask  covered  tightly  with  sacks 
and  a  wooden  cover.  Violent  boiling  immediately  takes  place.  When 
this  begins  to  subside  the  mixture  is  stirred  thoroughly  and  after  the 
boiling  stops  it  is  strained  into  the  spray  tank  and  diluted  to  the  proper 
strength. 

Recently  a  more  dilute  form  of  this  mixture  has  found  considerable 
use  for  fungicidal  purposes  for  application  to  trees  in  foliage  during 
the  summer  time.  This  is  made  in  a  similar  manner  to  that  just  de- 
scribed, using  10  pounds  of  lime  and  10  pounds  of  sulphur  to  50  gallons 
of  water. 

See  Circular  27,  Bureau  of  Plant  Industry.  U.  S.  D.  A. 

CONCENTRATED  LIME-SULPHUR. 

Another  method  of  preparing  the  lime-sulphur  spray  is  that  described 
in  Bulletin  306,  Geneva,  New  York  Experiment  Station. 

Formula : 

Lump  lime 60  pounds 

Sulphur   125  pounds 

Water    50  gallons 

This  is  mixed  in  a  kettle  and  cooked  over  a  fire,  according  to  the  first 
method  given  above,  boiling  for  one  or  more  hours.    After  the  cooking 


Bulletin  2181  CALIFORNIA  PLANT  DISEASES.  1187 

is  completed  the  clear  liquid  is  drawn  off  and  strained  and  water  added 
sufficient  to  make  the  required  50  gallons.  For  use,  5  gallons  of  this 
concentrated  liquid  is  diluted  with  45  gallons  of  water.  This  is  said 
to  be  safe  to  use  on  trees  when  the  buds  are  opening  or  even  in  full 
foliage. 

COMMERCIAL  LIME-SULPHUR. 

Several  commercial  preparations  of  lime-sulphur  are  now  on  the 
market  which  are  similar  in  nature  to  the  above.  These  are  concentrated 
mixtures  to  be  used  diluted  with  water.  There  is  no  reason  why  they 
should  not  be  effective  for  the  purposes  to  which  such  a  spray  is 
adapted  if  properly  prepared. 

OTHER  LIQUID  SULPHUR  SPRAYS. 

•  Sprays  somewhat  similar  to  the  above  are  sometimes  made  for 
fungicidal  purposes  by  boiling  sulphur  with  caustic  soda  or  potash  solu- 
tion.   The  following  formula  is  a  typical  one : 

Caustic  soda 12  pounds 

Sulphur  50  pounds 

Water    200  gallons 

Bring  the  soda  to  a  boil  in  a  kettle  of  water,  then  add  the  sulphur 
slowly  and  boil  with  frequent  stirring  for  about  an  hour.  Strain  the 
mixture  into  the  spray  tank  and  make  up  to  200  gallons.  Caustic  potash 
may  be  used  instead  of  soda. 

IRON  SULPHIDE  SPRAY. 

This  is  highly  recommended  by  Mr.  W.  H.  Volck,  County  Entomolo- 
gist of  Santa  Cruz  County,  as  a  fungicide  for  the  control  of  apple  mil- 
dew. The  process  of  preparing  this  material  is  quite  complicated  and 
is  one  which  would  scarcely  be  undertaken  by  the  average  grower.  A 
commercial  preparation  of  this  material  is  on  the  market. 

ADHESIVES. 

In  spraying  plants  with  a  smooth  or  waxy  surface,  such  as  onions, 
cabbage,  and  asparagus,  it  is  sometimes  useful  to  add  to  Bordeaux  mix- 
ture or  other  sprays  some  material  which  will  make  the  spray  liquid 
adhere  more  satisfactorily.  The  following  formula  is  useful  for  this 
purpose : 

Resin    2  pounds 

Sal  soda  crystals 1  pound 

Water    1  gallon 

Boil  in  a  kettle  until  the  mixture  becomes  a  clear,  amber  liquid.  Add 
this  amount  to  50  gallons  of  spray. 


1188  UNIVERSITY    OF    CALIFORNIA EXPERIMENT    STATION. 

SOAP. 

The  addition  of  4  or  5  pounds  of  whale-oil  or  other  cheap  soap  to 
each  50  gallons  of  Bordeaux  or  other  spray  is  quite  effective  in  increas- 
ing its  adhesive  qualities. 

LITERATURE. 

A  few  references  to  some  of  the  best  books  upon  the  subjects  treated 
in  this  bulletin  may  be  of  use  to  those  who  wish  to  obtain  more  detailed 
information  along  various  lines.  The  following  list  is  given  as  being 
well  adapted  to  the  general  reader : 

"Fungous  Diseases  of  Plants."     Dug-gar.     Published  by  Ginn  &  Company. 

"Diseases  of  Economic  Plants."  Stevens  &  Hall.  Published  by  The  Macmillan 
Company. 

"Diseases  of  Plants."     Tubeuf  &  Smith.     Published  by  Longmans  &  Company. 

"Disease  in  Plants."     Marshall  Ward.     Published  by  Macmillan  &  Company. 

"Text  Book  of  Botany,"  2  volumes.  Coulter,  Barnes  &  Cowles.  Published  by 
The  American  Book  Company. 

"California  Fruits."    Wickson.     Published  by  Pacific  Rural  Press  Company. 

"Soils."     Hilgard.     Published  by  The  Macmillan  Company. 


INDEX. 


Acid    soil    1066. 

Adhesives  1187. 

Air — relation   to  plant  growth   1047. 

Alfalfa. 

crown  gall  1079;  dodder  1083;  leaf  spot 
1079;  rust  1079;  stem  rot  1081. 

Almond. 

crown   gall   1084;    die  back   1086;   fruit 

drop  1084;   oak  fungus,   root  rot  1084; 

rust    1084;    shot-hole    1083;    sour    sap 

1085. 
Anaheim    disease. 

grape  1117. 

Apple. 

blight  1089;  climatic  effects  1093;  club 
tip  1093;  storage  spot  1092;  die  back, 
see  Almond;  fruit  spot  1092;  hollow 
1093;  little  leaf  1093;  mildew  1088; 
root  rot  1089;  scab  1089;  seasonal 
effects  1093;  stem  rot  1089;  sunburn 
1091;    toadstool   disease   1089. 

Apricot. 

blossom  rot  1097;  brown  rot  1097;  bud 
blight  1096;  climatic  effects  1098; 
crown  gall,  die  back,  fruit  drop,  see 
Almond;  fruit  spot  1095;  gummosis, 
see  Cherry;  root  rot,  see  Almond; 
scab  1097;  seasonal  effects  1098;  shot- 
hole  1095;  sour  sap  1098. 

Asparagus. 

rust    1100. 

Aster. 

yellows  1101. 
Atmospheric   effects,    injurious    1051. 
Bacteria,  general  acount  of,   1078. 
Bacteriosis. 

walnut  1172. 
Barley. 

leaf  spot  1102;  smut,  closed  and  loose 

1101. 

Bean. 

mildew  1102;   rust  1102;   spot  1102. 
Beet. 

blight    1104;    curly    top    1104;     downy 

mildew  1103;    eutettix   1104;   leaf   spot 

1102;    nematode    1104;    root  knot   1104; 

root  rot  1104;  rust  1102. 
Black  knot. 

grape  1115;  quince  1160;  walnut  1178. 
Black  leaf. 

pear  1155. 
Black  leg. 

potato  1158. 


Black  rot. 

cabbage  1108;  orange  1143;  sweet 
potato  1167. 

Black  spot, 
rose  1163. 

Blackberry. 

crown  gall  1107;  leaf  spot  1107;  rust 
1107;   soft  rot  1107. 

Blasting — to   loosen   soil    1074. 

Blight. 

apple  1094;  apricot  bud  blight  1089; 
beet  1104;  celery  1108;  lemon  1126; 
loquat  1130;  orange,  see  Lemon;  pea 
1149;  peach  1149;  pear  1154;  potato, 
early  blight,  1157;  late  blight  1157; 
quince,  see  Pear;  rose,  cane  blight 
1163;  sycamore  1167;  tomato,  summer 
blight  1168;  winter  blight  1168;  walnut. 
1172. 

Blosom   end  rot. 

tomato   1168. 

Blossom   rot. 

apricot   1097. 

Blue   mold. 

lemon  1126;  orange  1142. 

Bluestone    1183. 

Boll  rot. 

cotton  1111. 

Bordeaux   mixture   1185. 

Brown    rot. 

apricot  1097;  cherry  1109;  lemon  1122; 
orange,  see  Lemon;  peach  and  plum, 
see  Apricot. 

Brown  spot. 

orange    1143. 

Brown  streak. 

potato   1158. 

Brunissure. 

grape  1118. 

Bud  blight. 

apricot  1096. 

Cabbage. 

black  rot  1108;  club  foot  1108. 

California  yellows. 
peach    1151. 

Cane   blight, 
rose  1163. 

Carnation. 

leaf    spot    1108;    rust    1108;    stem    rot. 
1108;   wilt  1108. 


1190 


INDEX. 


Chemical   elements. 

deficiency  in  the  soil  1061. 

Celery. 

root  rot  1109;  stem  rot  1109;  summer 
blight  1108;   winter  blight  1108. 

Cement    dust    1060. 

Cherry. 

brown  rot  1109;  die  back  1110;  fruit 
drop  1110;  guramosis  1109;  root  rot 
1109. 

Chlorosis. 

orange  1137. 

Chrysanthemum, 
rust  1110. 

Citrus. 

diseases,  see  Lemon  and  Orange; 
peculiarities  1133. 

Climatic  conditions. 

irregular  1054;   relation   to  plant  1048. 

Climatic  effects. 

apple  1093;  apricot  1098. 

Club  foot. 

cabbage   1108. 

Club  tip. 

apple  1093. 

Cold    1051. 

Cold  storage  spot, 
apple  1092. 

Copper  carbonate  1184. 

Copper  sulphate   1183. 

Corn. 

mold  1111;  rust  1111;  smut  1110. 

Corrosive  sublimate  1184. 

Cotton. 

boll  rot  1111. 

Cottony  mold. 

lemon  1123. 

Coulure. 

grape  1117. 
Crater   blight. 

pear  1156. 
Crop  production,  ideal  conditions  for,  1041. 

Crown  gall. 

almond  1084;  apricot,  see  Almond; 
eucalyptus  1114;  nursery  stock  1131; 
peach  and  plum,  see  Almond;  walnut 
1178. 

Cucumber. 

leaf  spot  1112;  mildew  1111;  root  knot 
1112;  stem  rot  1111. 

Curly   bark, 
pear  1156. 

Curly  top. 
beet  1104. 

Currant. 

mildew   1112. 

Dahlia. 

mildew  1112. 


Damping   off. 

eucalyptus  1113;    lettuce   1130;    tomato 

1167. 
Dewberry,   see   Blackbery. 

Die    back. 

almond  1086;  apple  and  apricot,  see 
Almond;  cherry  1110;  orange,  Florida 
die  back  1136,  1139;  peach  and  plum, 
see  Almond;   walnut  1176. 

Disease. 

defined   1039;    causes   classified   1049. 

Dodder. 

alfalfa  1083. 

Downy   mildew. 

beet  1103;   onion  1133. 

Drop. 

lettuce   1130. 

Dry  rot. 

olive  1133;  potato  1156. 

Dryness. 

Atmospheric,       injurious      effects      of 

1055;   soil   1067. 
Dust   1060. 
Early  blight. 

potato  1157. 

Egg   plant. 

rot  1112;   stem  rot,  wilt  1113. 

Erinose. 

walnut  1176. 

Eucalyptus. 

crown  gall  1114;  damping  off  1113; 
leaf  spot  1113;  mildew  1113. 

Eutettix. 

beet  1104. 

Exanthema. 

orange  1136. 

Fertilization,  soil  1062. 

Florida    die-back. 

orange  1136. 
Fluids — movements   in   plants   1046. 

Folletage. 

grape  1118. 

Formalin   1184. 

Frizzles. 

pecan  1156. 

Frost  1051. 

protection  1052. 

Fruit  drop. 

almond  1084;  apricot,  see  Almond; 
cherry  1110;  peach,  see  Almond;  pear 
1156. 

Fruit  gumming, 
peach  1151. 
Fruit  spot. 

apple  1092;   apricot  1095. 
Fungi,  general  account  of,  1077. 
Fungicides  1183. 
Gas,  illuminating — injury  to  trees  1075. 


INDEX. 


1191 


Gopher   1075. 

Grape. 

Anaheim  disease  1117;  black  knot 
1115;  brunissure  1118;  coulure  1117; 
folletage  1118;  little  leaf  1117;  mildew 
1114;    red  leaf  1118;   rougeot  1118. 

Grape   fruit,    see    Orange. 

Grey  mold. 

lemon  1125. 

Guava. 

russeting  1119. 

Gummosis. 

apricot,  see  Cherry;  cherry  1109; 
lemon  1120;   orange,   see  Lemon. 

Hail    1057. 

Hardpan  1072. 
blasting  1074. 

Heat,    atmospheric,    injurious    effects    of, 
1053. 

Hollyhock. 

rust  1119. 

Hollow. 

apple  1093. 

Insects  1076. 

Introduction  1039. 

Iris. 

leaf  spot  1120. 

Iron  sulphide  1187. 
Late  blight, 
potato  115  f. 

Leaf. 

functions  of  1047;   respiration   in  1048. 

Leaf  curl. 

peach  llii). 

Leaf  gum   spot, 
orange  1142. 

Leaf  spot. 

alfalfa  1079;  barley  1102;  beet  1102; 
blackberry  1107;  carnation  1108;  cu- 
cumber 1112;  eucalyptus  1113;  iris 
1120;  madrone  1130;  oleander  1131; 
olive  1133;  palm,  date  1148;  palm, 
Washingtonia  1148;  strawberry  1166; 
tomato  1171;  vetch  1171. 
Lemon. 

blue    and    green    mold,    see    Orange 
brown    rot    1122;    cottony    mold    1123 
gray      mold      1125;      gummosis      1120 
peteca  1129;   red  rot  1129;   twig  blight 
1126;  wither- tip,  "tear  stain"  1127. 

Lettuce. 

damping  off  1130;  drop  1130. 

Lime   1183. 

Lime-sulphur  1186,    1187. 

Literature   1188. 

Little  leaf. 

apple  1093;  grape  1117;  peach  1151; 
quince,    see  Peach. 

Little   peach   1050. 

Little   potato   1158. 


Loganberry,  see  Blackberry. 

Loquat. 

blight   1130;    scab   1130. 

Madrone. 

leaf  spot  1130. 

Mai   di  gomma. 
orange   1136. 

Mildew. 

apple  1088;  bean  1102;  beet,  downy 
mildew  1103;  cucumber  1111;  currant 
1112;  dahlia  1112;  eucalyptus  1113; 
grape  1114;  onion,  downy  mildew 
1133;  pea  1149;  peach  1150;  pumpkin 
1160;  rose  1163;  strawberry  1166;  syca- 
more  1167. 

Moisture. 

atmospheric,  injurious  effects  of,  1055; 
excessive,  in  soil,  1071. 

Mold. 

corn  1111;  lemon,  grey  mold  1125; 
blue  mold,  see  Orange;  orange,  blue 
mold  1142. 

Moles    1075. 

Mottled    leaf. 

orange  1137. 
Navel   rot. 

orange  1143. 
Nematode. 

beet  1104;  nursery  stock  1131;  tomato 

1171. 

Nematode  worm   1076. 

Nursery  stock. 

crown  gall  1131;  nematode  1131;  root 
knot  1131. 

Oak  fungus. 

almond  1084. 

Oat. 

rust  1131;  smut  1131. 

Oleander. 

leaf  spot  1131;  twig  gall  1131. 

Olive. 

dry  rot  1133;  leaf  spot  1133;  root  rot 
and  toadstool,  see  Almond;  tubercu- 
losis. 1132. 

Onion. 

downy  mildew  1133. 

Orange. 

anthracnose  1140;  black  rot  1143;  blue 
mold  1142;  brown  rot,  see  Lemon; 
brown  spot  1143;  chlorosis  1137; 
damping  off  1141;  die  back  1139;  ex- 
anthema 1136;  Florida  die  back  1136; 
gummosis,  see  Lemon;  leaf  gum  spot 
1142;  mal  di  gomma  1136;  miscellane- 
ous spots  1146;  mottled  leaf  1137; 
navel  rot  1143;  puffing  1146;  root  rot 
1140;  scaly  bark  1135;  shoulder  spot 
1146;  stain  1146;  stem  end  spot  1146; 
splitting  1145;  tear  stain  1140;  toad- 
stool 1140;  trunk  rot  1140;  twig  blight, 
see  Lemon;   wither-tip  1140. 


1192 


INDEX. 


Palm,  date. 

leaf  spot  1148. 

Palm,    Washingtonia. 
leaf  spot  1148. 

Pea. 

blight  1149;   mildew  1149. 

Peach. 

blight  1149;  brown  rot,  see  Apricot 
California  yellows  1151;  crown  gall, 
die  back,  fruit  rot,  see  Almond;  fruit 
gumming  1151;  gummosis,  see  Cherry; 
leaf  curl  1149;  little  leaf  1151;  little 
peach  1150;  mildew  1150;  root  rot, 
rust,  sour  sap,  see  Almond;  split  pit 
1151;  yellows  1151. 

Pear. 

black  leaf  1155;  blight  1154;  crater 
blight  1156;  curly  bark  1156;  fruit 
drop  1156;  ringed  fruit  1156;  scab  1153. 

Pecan. 

rosette  or  frizzles  1156. 

Perforation. 

walnut  1175. 

Peteca. 

lemon   1129. 

Photosynthesis    1048. 

Physiological    diseases   1055. 

Plant. 

disease,  causes  classified  1049;  disease 
defined  1039;  disease,  directions  for 
examining  1049;  food,  substances  taken 
from  soil  1043;  growth,  factors  af- 
fecting 1040;  movement  of  fluids  in 
1046;  pathology,  scope  1040;  physiol- 
ogical diseases  1055;  physiology  1041; 
starch  formation  in  1048;  sugar  for- 
mation in  1048. 

Plum. 

brown  rot,  see  Apricot;  crown  gall, 
die  back,  rust,   sour  sap,  see  Almond. 

Pomelo,   see  Orange. 

Potash,   caustic  1185. 

Potassium  sulphide — liver  of  sulphur  1184. 

Potato. 

black  leg  1158;  brown  streak  1158; 
dry  rot  1158;  early  blight  1157;  gen- 
eral directions  for  planting  1159;  late 
blight  1157;  little  potato  1158;  scab 
1157. 

Pumpkin. 

mildew   1160;    wilt   1160. 

Prune. 

shrivels  1160;   see  Plum,   also. 

Puffing. 

orange  1146. 

Quince. 

black  knot  1160;  blight,  see  Pear;  lit- 
tle leaf,  see  Peach. 

Rabbits  1075. 


Red   leaf. 

grape   1118. 

Red   rot. 

lemon  1129. 

Resin    1188. 

Respiration. 

in   leaves  1047;    in   root  1044. 

Ringed   fruit, 
pear    1156. 

Root. 

functions  of  1044;   respiration   in  1044, 

Root    knot. 

beet  1104;  cucumber  1112;  nursery 
stock  1131;  peach,  see  Almond  crown 
gall;    tomato   1171. 

Koot   rot. 

almond  1084;  apple  1089;  apricot,  see 
Almond;  celery  1109;  cherry  1109; 
olive  1133;   orange  1140. 

Rose. 

black  spot  1163;  cane  blight  1163;  mil- 
dew 1163;  rust  1163. 

Rosette. 

pecan   1156. 

Rot. 

egg  plant  1112. 
Rougeot. 

grape  1118. 

Russeting. 

guava  1119. 

Rust. 

alfalfa  1079;  almond  1084;  asparagus 
1100;  bean  1102;  beet  1102;  black- 
berry 1107;  carnation  1108;  chrysan- 
themums 1110;  corn  1111;  hollyhock 
1119;  oat  1131;  peach  and  plum,  see 
Almond;   rose  1163;   wheat  1182. 

Saline  water,  irrigation  with,  1065. 

Santa    Ana    1053. 

Scab. 

apple  1089;  apricot  1097;  loquat  1130; 
pear  1153;  potato  1157. 

Scaly   bark, 
orange  1135. 

Seasonal    effects. 

apple  1093;  apricot  1098. 

Shot  hole. 

almond  1083;    apricot   1095. 

Shoulder  spot, 
orange  1146. 

Shrivels. 

prune    1160. 

Slime    molds    1079. 

Slugs    1076. 

Smelter  fumes  1058. 

Smut. 

barley  1101;  corn  1110;  oat  1131;  sor- 
ghum 1166;   wheat  1182. 


INDEX. 


1193 


Soap,   1188. 

Soda,  caustic  1185. 

Soft   rot. 

blackberry  1107;  sweet  potato  1167. 

Soil. 

acid  1066;  alkali  1063;  artificial  sub- 
stances in  1074;  chemical  deficiency 
1061;  chemical  nature  1045;  chemical, 
physical  and  biological  relation  to 
plant  growth  1043;  deficiencies  1061; 
dryness  1067;  excess  of  water  1071; 
faulty  structure  1072;  fertilization 
1062;  water  deficiency  1061,  1067. 

Sorghum. 

smut  1166. 

Sour  sap. 

almond  1085;  apricot  1098;  peach  and 
plum,   see  Almond. 

Split  pit. 

peach  1151. 

Splitting. 

orange  1145. 
Spot. 

bean  1102;  orange,  leaf  gum  spot 
1142;  miscellaneous  spots,  shoulder 
spot,   stem  end  spot  1146. 

Squash,    see    Pumpkin. 

Squirrels  1075. 

Stain. 

orange  1146. 

Starch — formation  in  plant  1048. 

Stem  end  spot. 

orange   1146. 
Stem    rot. 

alfalfa     1081;     apple     1089;     carnation 

1108;  celery  1109;  cucumber  1111;  egg 

plant  1113;    tomato   1170. 

Strawberry. 

leaf  spot  1166;   mildew  1166. 

Subsoil,   dry  1069. 

Subsoil,  faulty  structure  1072. 

Sugar,    formation   in  plant   1048. 

Sulphur   1183. 
sprays  1186. 

Summer  blight. 

celery  1108;  tomato  1168. 

Sunburn  1053. 

apple  1091;  prevention  of  1054;  wal- 
nut 1175. 

Sunscald    1053. 
Sweet  potato. 

black    rot    1167;    stem    rot    1167;    soft 

rot  1167;   wilt  1167. 


Sycamore. 

blight   1167;    mildew   1167. 

Toadstool   disease. 

almond,  see  Root  rot  1084;  apple  1089; 
olive,    see   Almond;    orange    1140. 

Tomato. 

blossom  end  rot  1168;  damping  off 
1167;  leaf  spot  1171;  nematode  1171; 
root  knot  1171;  stem  rot  1170;  summer 
blight  1168;  winter  blight  1168. 

Trunk  rot. 

orange  1140;   walnut  1173. 

Tuberculosis, 
olive  1132. 

Turnip,    see    Cabbage. 

Twig   blight. 

lemon  1126;   orange,    see  Lemon. 

Twig   gall. 

oleander  1131. 

Vetch. 

leaf  spot  1171. 

Walnut. 

bacteriosis  1172;  black  knot  1178; 
blight  1172;  crop  failure  1179;  crown 
gall  1178;  die  back  1176;  erinose  1176; 
perforation  1175;  sunburn  1175;  trunk 
rot   1173;   yellows   1178. 

Water. 

alkali,  irrigation  with  1064;  alkali, 
rise  of,  in  soil  water  1065;  deficiency 
in  soil  1061,  1067;  excessive,  in  soil 
1071;  fluctuating  level  in  soil  1071; 
saline,    irrigation   with  1065. 

Watermelon, 
wilt   1181. 

Wheat. 

closed  smut  1181;  loose  smut  1181; 
rust  1181;   yellows  1182. 

White  rot. 

lemon   1123. 

Wilt. 

carnation  1108;  egg  plant  1113;  pump- 
kin 1160;   watermelon   1181. 

Wind,  injurious  effects  of,   1056. 
Wind-breaks   1057. 
Winter  blight. 

celery  1108;  tomato  1168. 

Wither-tip. 

lemon  1127;  orange  1140. 

Worm,    Nematode    1089. 

Yellows. 

aster  1101;  peach,  California  yellows 
1151;  walnut  1178;  wheat  1182. 


STATION    PUBLICATIONS   AVAILABLE   FOR    DISTRIBUTION. 


REPORTS. 

1896.  Report  of  the  Viticultural  Work  during  the  seasons  1887-93,  with  data  regard- 

ing the  Vintages  of  1894-95. 

1897.  Resistant  Vines,  their  Selection,  Adaptation,  and  Grafting.     Appendix  to  Viti- 

cultural Report  for  1896. 

1902.  Report   of   the   Agricultural   Experiment   Station   for    1898-1901. 

1903.  Report  of  the  Agricultural  Experiment  Station  for   1901-03. 

1904.  Twenty-second  Report  of  the  Agricultural  Experiment  Station  for  1903-04. 


BULLETINS. 


Reprint.  Endurance    of    Drought    in    Soils 

of   the   Arid   Region. 
No.   128.  Nature,    Value,     and    Utilization 
of  Alkali  Lands,  and  Tolerance 
of   Alkali.       (Revised   and   Re- 
print,   1905.) 

133.  Tolerance    of   Alkali   by   Various 
Cultures. 

147.   Culture    Work    of    the     Sub-sta- 
tions. 

149.  California    Sugar    Industry. 

151.  Arsenical    Insecticides. 

153.   Spraying  with   Distillates. 

159.  Contribution     to     the     Study     of 
Fermentation. 

162.  Commercial       Fertilizers.        (De- 
cember 1,   1904.) 

165.  Asparagus   and    Asparagus    Rust 
in    California. 

167.  Manufacture    of    Dry    Wines    in 

Hot   Countries. 

168.  Observations  on   Some  Vine  Dis- 
eases   in    Sonoma    County. 

169.  Tolerance  of  the  Sugar  Beet  for 

Alkali. 

170.  Studies    in    Grasshopper    Control. 

171.  Commercial     Fertilizers.        (June 

30,    1905.) 

172.  Further  Experience  in  Asparagus 

Rust    Control. 
174.  A  New  Wine-cooling  Machine. 

176.  Sugar  Beets  in  the   San  Joaquin 

Valley. 

177.  A   New   Method    of  Making   Dry 

Red  Wine. 

178.  Mosquito  Control. 

179.  Commercial    Fertilizers.       (June, 

1906.) 

180.  Resistant  Vineyards. 

181.  The   Selection  of  Seed-Wheat. 

182.  Analysis     of     Paris     Green     and 

Lead  Arsenic.     Proposed  Insec- 
ticide Law. 

183.  The  California  Tussock-moth. 

184.  Report  of  the   Plant   Pathologist 

to   July   1,    1906. 

185.  Report     of     Progress     in     Cereal 

Investigations. 

186.  The  Oidium  of  the  Vine. 

187.  Commercial    Fertilizers.       (Janu- 

ary,  1907.) 


No.   188. 

189. 

190. 
191. 
192. 

193. 


194. 

195. 

197. 


198. 
199. 
200. 

201. 

202. 

203. 

204. 

205. 

206. 

207. 

208. 
209. 
210. 

211. 

212. 
213. 
214. 
215. 

216. 
217. 


Lining  of  Ditches  and  Reservoirs 
to  Prevent  Seepage  and  Losses. 

Commercial  Fertilizers.  (June, 
1907.) 

The  Brown  Rot  of  the  Lemon. 

California    Peach    Blight. 

Insects  Injurious  to  the  Vine  in 
California. 

The  Best  Wine  Grapes  for  Cali- 
fornia ;  Pruning  Young  Vines ; 
Pruning  the  Sultanina. 

Commercial  Fertilizers.  (De- 
cember,   1907.) 

The  California  Grape  Root-worm. 

Grape  Culture  in  California ; 
Improved  Methods  of  Wine- 
making  ;  Yeast  from  California 
Grapes. 

The  Grape  Leaf-Hopper. 

Bovine  Tuberculosis. 

Gum  Diseases  of  Citrus  Tres  in 
California. 

Commercial  Fertilizers.  (June, 
1908.) 

Commercial  Fertilizers.  (De- 
cember,   1908.) 

Report  of  the  Plant  Pathologist 
to   July   1,    1909. 

The  Dairy  Cow's  Record  and  the 
Stable. 

Commercial  Fertilizers.  (De- 
cember,   1909.) 

Commercial  Fertilizers.  (June, 
1910.) 

The  Control  of  the  Argentine 
Ant. 

The  Late  Blight  of  Celery. 

The  Cream   Supply. 

Imperial  Valley  Settlers'  Crop 
Manual. 

How  to  Increase  the  Yield  of 
Wheat    in    California. 

California  White  Wheats. 

The    Principles   of  Wine-Making. 

Citrus    Fruit    Insects. 

The  Housefly  in  Its  Relation  to 
Public  Health. 

A  Progress  Report  Upon  Soil  and 
Climatic  Factors  in  Influencing 
the   Composition   of  Wheat. 

Honey   Plants  of  California. 


CIRCULARS. 


No.   1.  Texas    Fever. 

5.   Contagious  Abortion  in  Cows. 
7.  Remedies  for  Insects. 
9.  Asparagus    Rust. 

11.  Fumigation  Practice. 

12.  Silk  Culture. 

15.   Recent     Problems     in     Agriculture. 
What  a  University  Farm  is  For. 
19.   Disinfection  of  Stables. 
29.   Preliminary     Announcement     Con- 
cerning   Instruction    in    Practical 
Agriculture   upon   the   University 
Farm,  Davis,  Cal. 
White  Fly  in  California. 
White   Fly   Eradication. 
33.   Packing     Prunes     in     Cans.       Cane 
Sugar  vs.   Beet  Sugar. 
Analyses    of    Fertilizers    for    Con- 
sumers. 
Instruction     in     Practical    Agricul- 
ture at  the  University  Farm. 
Suggestions    for    Garden    Work    in 
California    Schools. 

47.  Agriculture  in  the  High  Schools. 

48.  Butter  Scoring  Contest,   1909. 

49.  Insecticides. 

50.  Fumigation  Scheduling. 


30 
32 


36. 


39. 


46. 


No.   51.  University  Farm   School. 

52.  Information  for  Students  Concern- 

ing the  College  of  Agriculture. 

53.  Announcement   of  Farmers'    Short 

Courses  for   1910. 

54.  Some     Creamery     Problems     and 

Tests. 

55.  Farmers'    Institutes  and   Universit 

Extension    in    Agriculture. 

57.  Announcement  of   Farmers'    Short 

Courses  in  Animal  Industry  and 
Veterinary  Science. 

58.  Experiments  with  Plants  and  Soils 

in      Laboratory,      Garden,      and 
Field. 

59.  Tree      Growing      in      the      Public 

Schools. 

60.  Butter  Scoring  Contest,   1910. 

61.  University   Farm    School. 

62.  The   School  Garden  in  the  Course 

of  Study. 

63.  How     to     Make     an     Observation 

Hive. 

64.  Announcement   of   Farmers'    Short 

Courses  for  1911. 

65.  Calif ornin.   Insecticide  Law. 

66.  Insecticides  and  Insect  Control. 


